HISTOLOGY OF 
MEDICINAL PLANTS 



BY 

WILLIAM MANSFIELD, A.M., Phar.D. 

Professor of Histology and Pharmacognosy, College of 
Pharmacy of the City of New York 
Columbia University 



FIRST EDITION 
FIRST THOUSAND 



NEW YORK 
JOHN WILEY & SONS, Inc. 

London: CHAPMAN & HALL, Limited 
1916 



Copyright, 1 91 6, by 
WILLIAM MANSFIELD 



OCT -6 19(6 



Publishers Printing Company 
207-217 West Twenty-fifth Street, New York 



©CI.A445051 

"Mb ( 



PREFACE 



The object of the book is to provide a practical scientific 
course in vegetable histology for the use of teachers and students 
in schools and colleges. 

The medicinal plants are studied in great detail because 
they constitute one of the most important groups of economic 
plants. The cells found in these plants are typical of the cells 
occurring in the vegetable kingdom.; therefore the book should 
prove a valuable text-book for all students of histology. 

The book contains much that is new. In Part II, which is 
devoted largely to the study of cells and cell contents, is a new 
scientific, yet practical, classification of cells and cell contents. 
The author believes that his classification of bast fibres and 
hairs will clear up much of the confusion that students have 
experienced when studying these structures. 

The book is replete with illustrations, all of which are from 
original drawings made by the author. As most of these illus- 
trations are diagnostic of the plants in which they occur, they 
will prove especially valuable as reference plates. 

The material of the book is the outgrowth of the experience 
of the author in teaching histology at the College of Pharmacy 
of the City of New York, Columbia University, and of years 
of practical experience gained by examining powdered drugs in 
the laboratory of a large importing and exporting wholesale 
drug house. 

The author is indebted to Ernest Leitz and Bausch & 
Lomb Optical Company for the use of cuts of microscopic 
apparatus used in Part I of the book. 

The author also desires to express his appreciation to Pro- 
fessor Walter S. Cameron, who has rendered him much valuable 
aid. 

William Mansfield. 

Columbia University, 
September, 191 6. 



iii 



CONTENTS 



PART I 

Simple and Compound Microscopes and Micro- 
scopic Technic 

CHAPTER I 
THE SIMPLE MICROSCOPES 

PAGE 

Simple microscopes, forms of . . . . 4 

CHAPTER II 
COMPOUND MICROSCOPES 

Compound microscopes, structure of 7 

Compound microscopes, mechanical parts of 7 

Compound microscopes, optical parts of 9 

Compound microscopes, forms of 12 

CHAPTER III 

MICROSCOPIC MEASUREMENTS 

Ocular micrometer 19 

Stage micrometer 19 

Mechanical stage 1 21 

Micrometer eye-pieces 21 

Camera lucida 22 

Drawing apparatus 23 

Microphotographic apparatus 24 

CHAPTER IV 

HOW TO USE THE MICROSCOPE 

Illumination 26 

Micro lamp 27 

Care of the microscope 28 

Preparation of specimens for cutting 28 

v 



Vi CONTENTS 

PAGE 

Paraffin imbedding oven 30 

Paraffin blocks 31 

Cutting sections 31 

Hand microtome 31 

Machine microtomes 32 

CHAPTER V 

REAGENTS 

Reagent set . 39 

Measuring cylinder 40 

CHAPTER VI 

HOW TO MOUNT SPECIMENS 

Temporary mounts 41 

Permanent mounts 41 

Cover glasses 43 

Glass slides 44 

Forceps . 45 

Needles 46 

Scissors 46 

Turntable 46 

Labeling 47 

Preservation of mounted specimens 48 

Slide box 48 

Slide tray 48 

Slide cabinet 49 

PART II 

Tissues, Cells and Cell Contents 

CHAPTER I 

THE CELL 

Typical cell _ . 53 

Changes in a cell undergoing division 55 

Origin of multicellular plants . 57 

CHAPTER II 

THE EPIDERMIS AND PERIDERM 

Leaf epidermis 59 

Testa epidermis 63 

Plant hairs . 66 



CONTENTS vii 

PAGE 

Forms of hairs 67 

Papillae 67 

Unicellular hairs 69 

Multicellular hairs 72 

Periderm . 80 

Cork periderm 80 

Stone cell periderm 85 

Parenchyma and stone cell periderm 85 

CHAPTER III 

MECHANICAL TISSUES 

Bast fibres . 89 

Crystal bearing bast fibres 90 

Porous and striated bast fibres 92 

Porous and non-striated bast fibres 96 

Non-porous and striated bast fibres 96 

Non-porous and non-striated bast fibres 96 

Occurrence of bast fibres in powdered drugs 103 

Wood fibres 104 

Ccllenchyma cells 106 

Stone cells .................. 109 

Endodermal cells 116 

Hypodermal cells 118 

CHAPTER IV 

ABSORPTION TISSUE 

Root hairs 121 

CHAPTER V 

CONDUCTING TISSUE 

Vessels and tracheids 126 

Annular vessels 127 

Spiral vessels 127 

Sclariform vessels 128 

Reticulate vessels 131 

Pitted vessels 131 

Pitted vessels with bordered pores 131 

Sieve tubes < 136 

Sieve plate . 138 

Medullary bundles, rays and cells 138 

Medullary ray bundle 139 

The medullary ray 139 

The medullary ray cell 141 



viii 



CONTEXTS 



PAGE 

Structure of the medullary ray cells . 142 

Arrangement of the medullary ray cells in the medullary ray . . . 142 

Latex tubes 

Parenchyma 

Cortical parenchyma 147 

Pith parenchyma 147 

Leaf parenchyma 150 

Aquatic plant parenchyma 150 

Wood parenchyma 150 

Phloem parenchyma . 150 

Palisade parenchyma 150 

CHAPTER VI 
AERATING TISSUE 

Water pores .151 

Stomata 151 

Relation of stomata to the surrounding cells 154 

Lenticels , 157 

Intercellular spaces 158 

CHAPTER VII 

SYNTHETIC TISSUE 

Photosynthetic tissue . 163 

Glandular tissue 164 

Glandular hairs 164 

Secretion cavities 166 

Schizogenous cavities . 168 

Lysigenous cavities 168 

Schizo-lysigenous cavities 168 

CHAPTER VIII 

STORAGE TISSUE 

Storage cells 173 

Storage cavities . . . .1 . . . . 176 

Crystal cavities 176 

Mucilage cavities .176 

Latex cavities 176 

Oil cavity .". . 178 

Glandular hairs as storage organs 178 

Storage walls 179 



CONTENTS ix 

CHAPTER IX 
CELL CONTENTS 

PAGE 

Chlorophyll 182 

Leucoplastids 183 

Starch grains 183 

Occurrence . . .... . 184 

Outline 185 

Size 185 

Hilum 185 

Nature of hilum 188 

Inulin 194 

Mucilage . 194 

Hesperidin 196 

Volatile oil • • 196 

Tannin 196 

Aleurone grains 197 

Structure of aleurone grains 197 

Form of aleurone grains ,.197 

Description of aleurone grains 198 

Tests for aleurcne grains 198 

Crystals 200 

Micro-crystals 200 

Raphides 200 

Rosette crystals 202 

Solitary crystals 205 

Cystoliths 210 

Forms of cystoliths 210 

Tests for cystoliths 215 



PART III 

Histology of Roots, Rhizomes, Stems, Barks, 
Woods, Flowers, Fruits and Seeds 

CHAPTER I 
ROOTS AND RHIZOMES 



Cross-section of pink root 219 

Cross-section of ruellia root 219 

Cross-section of spigelia rhizome 223 

Cross-section of ruellia rhizome 226 

Powdered pink root . 227 

Powdered ruellia root 227 



X 



CONTENTS 



CHAPTER II 

STEMS 

PAGE 

Herbaceous stems 233 

Cross-section, spigelia stem 233 

Ruellia stem 235 

Powdered horehound 237 

Powdered spurious horehound 237 

Insect flower stems 241 

CHAPTER III 

WOODY STEMS 

Buchu stem 242 

Mature buchu stem 242 

Powdered buchu stem 245 

CHAPTER IV 

BARKS 

White pine bark 248 

Powdered white pine bark 250 

CHAPTER V 

WOODS 

Cross-section quassia 254 

Radial-section quassia 254 

Tangential-section quassia 258 

CHAPTER VI 

LEAVES 

Klip buchu 260 

Powdered klip buchu 262 

Mountain laurel 264 

Trailing arbutus 264 

CHAPTER VII 

FLOWERS 

Pollen grains 270 

Non-spiny- walled pollen grains 273 

Spiny- walled pollen grains 273 

Stigma papillae . - 274 



CONTENTS xi 

PAGE 

Powdered insect flowers 278 

Open insect flowers 280 

Powdered white daisies 282 

CHAPTER VIII 
FRUITS 

Celery fruit 285 

CHAPTER IX 

SEEDS 

Sweet almonds 289 

CHAPTER X 

ARRANGEMENT OF VASCULAR BUNDLES 

Types of fibro-vascular bundles 292 

Radial vascular bundles 292 

Concentric vascular bundles 295 

Collateral vascular bundles 295 

Bi-collateral vascular bundles 298 

Open collateral vascular bundles 298 



Part I 



SIMPLE AND COMPOUND MICROSCOPES 
AND MICROSCOPIC TECHNIC 



CHAPTER I 



THE SIMPLE MICROSCOPES 

The construction and use of the simple microscope (magni- 
fiers) undoubtedly date back to very early times. There is 
sufficient evidence to prove that spheres of glass were used as 
burning spheres and as magnifiers by people antedating the 
Greeks and Romans. 

The simple microscopes of to-day have a very wide range of 
application and a corresponding variation in structure and in 
appearance. 

Simple microscopes are used daily in classifying and studying 
crude drugs, testing linen and other cloth, repairing watches, 
in reading, and identifying insects. The more complex simple 
microscopes are used in the dissection and classification of 
flowers. 

The watchmaker's loupe, the linen tester, the reading glass, 
the engraver's lens, and the simplest folding magnifiers consist 
of a double convex lens. Such a lens produces an erect, en- 
larged image of the object viewed when the lens is placed so 
that the object is within its focal distance. The focal distance 
of a lens varies according to the curvature of the lens. The 
greater the curvature, the shorter the focal distance and the 
greater the magnification. 

The more complicated simple microscope consists of two or 
more lenses. The double and triple magnifiers consist of two 
and three lenses respectively. 

When an object is viewed through three lenses, the magnifi- 
cation is greater than when viewed through one or two lenses, 
but a smaller part of the object is magnified. 



4 



HISTOLOGY OF MEDICINAL PLANTS 



FORMS OF SIMPLE MICROSCOPES 

TRIPOD MAGNIFIER 

The tripod magnifier (Fig. i) is a simple lens mounted on a 
mechanical stand. The tripod is placed over the object and 
the focus is obtained by means of a screw which raises or lowers 
the lens, according to the degree it is magnified. 

watchmaker's loupe 

The watchmaker's loupe (Fig. 2) is a one-lens magnifier 
mounted on an ebony or metallic tapering rim, which can be 




Fig. 1. — Tripod Magnifier Fig. 2. — Watchmaker's Loupe 

placed over the eye and held in position by frowning or con- 
tracting the eyelid. 

FOLDING MAGNIFIER 

The folding magnifier (Fig. 3) of one or more lenses is mounted 
in such a way that, when not in use, the lenses fold up like the 




Fig. 3. — Folding Magnifier Fig. 4. — Reading Glass 



blade of a knife, and when so folded are effectively protected 
from abrasion by the upper and lower surfaces of the folder. 

READING GLASSES 

Reading glasses (Fig. 4) are large simple magnifiers, often 
six inches in diameter. The lens is encircled with a metal band 
and provided with a handle. 



THE SIMPLE MICROSCOPES 



5 



STEINHEIL APLANATIC LENSES 



Steinheil aplanatic lenses (Fig. 5) consist of three or four 
lenses cemented together. The combination is such that the 
field is large, flat, and achromatic. These lenses are suitable 




Fig. 5. — Steinheil Aplanatic Lens 

for field, dissecting, and pocket use. When such lenses are 
placed in simple holders, they make good dissecting microscopes. 



DISSECTING MICROSCOPE 



The dissecting microscope (Fig. 6) consists of a Steinheil 
lens and an elaborate stand, a firm base, a pillar, a rack and 




Fig. 6. — Dissecting Microscope 



6 



HISTOLOGY OF MEDICINAL PLANTS 



pinion, a glass stage, beneath which there is a groove for holding 
a metal plate with one black and one white surface. The 
nature of the object under observation determines whether a 
plate is used. When the plate is used and when the object is 
studied by reflected light it is sometimes desirable to use the 
black and sometimes the white surface. The mirror, which has 
a concave and a plain surface, is used to reflect the light on the 
glass stage when the object is studied by transmitted light. 
The dissecting microscope magnifies objects up to twenty 
diameters, or twenty times their real size. 



CHAPTER II 



COMPOUND MICROSCOPES 

The compound microscope has undergone wonderful changes 
since 1667, the days of Robert Hooke. When we consider the 
crude construction and the limitations of Robert Hooke 's micro- 
scope, we marvel at the structural perfection and the unlimited 
possibilities of the modern instrument. The advancement made 
in most sciences has followed the gradual perfection of this 
instrument. 

The illustration of Robert Hooke's microscope (Fig. 7) will 
convey to the mind more eloquently than words the crudeness 
of the early microscopes, especially when it is compared with 
the present-day microscopes. 

STRUCTURE OF THE COMPOUND MICROSCOPE 

The parts of the compound microscope (Fig. 8) may be 
grouped into — first, the mechanical, and, secondly, into the 
optical parts. 

THE MECHANICAL PARTS 

1. The foot is the basal part, the part which supports all 
the other mechanical and optical parts. The foot should be 
heavy enough to balance the other parts when they are inclined. 
Most modern instruments have a three-parted or tripod- 
shaped base. 

2. The pillar is the vertical part of the microscope attached 
to the base. The pillar is joined to the limb by a hinged joint. 
The hinges make it possible to incline the microscope at any 
angle, thus lowering its height. In this way, short, medium, 
and tall persons can use the microscope with facility. The 
part of the pillar above the hinge is called the limb. The limb 
may be either straight or curved. The curved form is pref- 
erable, since it offers a more suitable surface to grasp in trans- 
ferring from box or shelf to the desk, and vice versa. 

7 



HISTOLOGY OF MEDICINAL PLANTS 




Fig. 7. — Compound Microscope of Robert Hooke 



COMPOUND MICROSCOPES 



9 



3. The stage is either stationary or movable, round or 
square, and is attached to the limb just above the hinge. The 
upper surface is made of a composition which is not easily 
attacked by moisture and reagents. The centre of the stage is 
perforated by a circular opening. 

4. The sub-stage is attached below the stage and is for the 
purpose of holding the iris diaphragm and Abbe condenser. 
The raising and lowering of the sub-stage are accomplished by 
a rack and pinion. 

5. The iris diaphragm, which is held in the sub-stage below 
the Abbe condenser, consists of a series of metal plates, so ar- 
ranged that the light entering the microscope may be cut off 
completely or its amount regulated by moving a control pin. 

6. The fine adjustment is located either at the side or at 
the top of the limb. It consists of a fine rack and pinion, and 
is used in focusing an object when the low-power objective is in 
position, or in finding and focusing the object when the high- 
power objective is in position. 

7. The coarse adjustment is a rack and pinion used in raising 
and lowering the body-tube and in finding the approximate 
focus when either the high- or low-power objective is in position. 

8. The body-tube is the path traveled by the rays of light 
entering the objectives and leaving by the eye-piece. To the 
lower part of the tube is attached the nose-piece, and resting 
in its upper part is the draw-tube, which holds the eye-piece. 
On the outer surface of the draw-tube there is a scale which 
indicates the distance it is drawn from the body-tube. 

9. The nose-piece may be simple, double, or triple, and it 
is protected from dust by a circular piece of metal. Double and 
triple nose-pieces may be revolved, and like the simple nose- 
piece they hold the objectives in position. 

THE OPTICAL PARTS 

i . The mirror is a sub-stage attachment one surface of which 
is plain and the other concave. The plain surface is used with 
an Abbe condenser when the source of fight is distant, while 
the concave surface is used with instruments without an Abbe 
condenser when the source of light is near at hand. 



HISTOLOGY OF MEDICINAL PLANTS 




p IG> g — Compound Microscope 



COMPOUND MICROSCOPES 



11 



2. The Abbe condenser (Fig. 9) is a combination of two or 
more lenses, arranged so as to concentrate the light on the 
specimen placed on the stage. The condenser is located in the 
opening of the stage, and its uppermost 

surface is circular and flat. 

3. Objectives (Figs. 10, 11, and 12). 
There are low, medium, and high-power 
objectives. The low-power objectives have 
fewer and larger lenses, and they magnify 
least, but they show more of the object than 
do the high-power objectives. 

There are three chief types of objec- 
tives: First, dry objectives; second, wet 
objectives, of which there are the water-immersion objec- 
tives; and third, the oil-immersion objectives. The dry 
objectives are used for most histological and pharmacog- 
nostical work. For studying smaller objects the water ob- 




FiG. 9. — Abbe 
Condenser 




Fig. 10. 




Fig. 11. 
Objectives. 




Fig. 12. 



jective is sometimes desirable, but in bacteriological work the 
oil-immersion objective is almost exclusively used. The globule 
of water or oil, as the case may be, increases the amount of light 
entering the objective, because the oil and water bend many 
rays into the objective which would otherwise escape. 

4. Eye-pieces (Figs. 13, 14, and 15) are of variable length, 
but structurally they are somewhat similar. The eye-piece 
consists of a metal tube with a blackened inner tube. In the 



12 



HISTOLOGY OF MEDICINAL PLANTS 



centre of this tube there is a small diaphragm for holding the 
ocular micrometer. In the lower end of the tube a lens is fas- 
tened by means of a screw. This, the field lens, is the larger 
lens of the ocular. The upper, smaller lens is fastened in the 




Fig. 14. Fig. 15. 

Eye-Pieces. 



tube by a screw, but there is a projecting collar which rests, 
when in position, on the draw-tube. 

The longer the tube the lower the magnification. For 
instance, a two-inch ocular magnifies less than an inch and a 
half, a one-inch less than a three-fourths of an inch, etc. 

The greater the curvature of the 
lenses of the ocular the higher will be 
the magnification and the shorter the 
tube-length. 

FORMS OF COMPOUND 
MICROSCOPES 

The following descriptions refer to 
three different models of compound 
microscopes: one which is used chiefly 
as a pharmacognostic microscope, one 
as a research microscope stand, while 
the third type represents a research 
microscope stand of highest order, 
which is used at the same time for 
taking microphotographs. 

PHARMACOGNOSTIC MICROSCOPE 

Fig. i6.-Pharmacognostic . The pharmacognosy microscope 

Microscope (Fig. 16) is an instrument which 




COMPOUND MICROSCOPES 



13 



embodies only those parts which are most essential for the 
examination of powdered drugs, bacteria, and urinary 
sediments. This microscope is provided with a stage of the 
dimensions 105 x 105 mm. This factor and the distance of 
80 mm. from the optical centre to the handle arm render it 
available for the examination of even very large objects and 
preparations, or preparations suspended in glass dishes. The 
stand is furnished with a side micrometer, a fine adjustment 
having knobs on both sides, thereby permitting the manipula- 
tion of the micrometer screw either by left or right hand. The 
illuminating apparatus consists of the Abbe condenser of numeri- 
cal aperture of 1.20, to which is attached an iris diaphragm for 
the proper adjustment of the light. A worm screw, mounted 
in connection with the condenser, serves for the raising and 
lowering of the condenser, so that the cone of illuminating 
pencils can be arranged in accordance to the objective employed 
and to the preparation under observation. The objectives 
necessary are those of the achromatic type, possessing a focal 
length of 16.2 mm. and 3 mm. Oculars which render the best 
results in regard to magnification in connection with the two 
objectives mentioned are the Huyghenian eye-pieces II and IV 
so that magnifications are obtained varying from 62 to 625. 
It is advisable, however, to have the microscope equipped with 
a triple revolving nose-piece for the objectives, so that provision 
is made for the addition of an oil-immersion objective at any 
time later should the microscope become available for bac- 
teriological investigations. 

THE RESEARCH MICROSCOPE 

The research microscope used in research work (Fig. 17) must 
be equipped more elaborately than the microscope especially 
designed for the use of the pharmacognosist. While the simple 
form of microscope is supplied with the small type of Abbe 
condenser, the research microscope is furnished with a large 
illuminating apparatus of which the iris diaphragm is mounted 
on a rack and pinion, allowing displacement obliquely to the 
optical centre, also to increase resolving power in the objectives 
when observing those objects which cannot be revealed to the 
best advantage with central illumination. Another iris is 



14 



HISTOLOGY OF MEDICINAL PLANTS 



furnished above the condenser; this iris becomes available the 
instant an object is to be observed without the aid of the con- 
denser, in which case the upper iris diaphragm allows proper 
adjustment of the light. The mirror, one side plane, the other 
concave, is mounted on a movable bar, along which it can 
be slid — another convenience for the adjustment of the light. 
The microscope stage of this stand is of the round, rotating 




Fig. 17. — Research Fig. 18. — Special 

Microscope Research Microscope 



and centring pattern, which permits a limited motion to the 
object slide. The rotation of the microscope stage furnishes 
another convenience in the examination of objects in polarized 
light, allowing the preparation to be rotated in order to 
distinguish the polarization properties of the objects under 
observation. 

SPECIAL RESEARCH MICROSCOPE 

A special research microscope of the highest order (Fig. 18) 
is supplied with an extra large body tube, which renders it of 



COMPOUND MICROSCOPES 



15 



special advantage for micro-photography. Otherwise in its 
mechanical equipment it resembles very closely the medium- 
sized research microscope stand, with the exception that the 
stand is larger in its design, therefore offering universal applica- 
tion. In regard to the illuminating apparatus, it is advisable 
to mention that the one in the large research microscope stand 
is furnished with a three-lens condenser of a numerical aperture 
of 1.40, while the medium-sized research stand is provided with 
a two-lens condenser of a numerical aperture of 1.20. The 
stage of the microscope is provided with a cross motion — the 
backward and forward motion of the preparation is secured by 
rack and pinion, while the side motion 
is controlled by a micrometric worm 
screw. In cases where large prepa- 
rations are to be photographed, the 
draw-tube with ocular and the slider 
in which the draw-tubes glide are 
removed to allow the full aperture 
of wide-angle objectives to be made 
use of. 

BINOCULAR MICROSCOPE 

The Gre enough binocular micro- 
scope, as shown in Fig. 19, consists 
of a microscope stage with two tubes 
mounted side by side and moving on 
the same rack and pinion for the 
focusing adjustment. Either tube 
can be used without the other. The 
oculars are capable of more or less 
separation to suit the eyes of different 
observers. In each of the drub-like 
mountings, near the point where the 
oculars are introduced, porro-prisms 

have been placed, which erect the image. This microscope 
gives most perfect stereoscopic images, which are erect instead 
of inverted, as in the monocular compound microscopes. The 
Greenough binocular microscope is especially adapted for dis- 
section and for studying objects of considerable thickness. 




Fig. 19. — Greenough 
Binocular Microscope 



16 



HISTOLOGY OF MEDICINAL PLANTS 



POLARIZATION MICROSCOPE 

The polarization microscope (Fig. 20) is used chiefly for the 
examination of crystals and mineral sections as well as for the 
observation of organic bodies in polarized light. It can, how- 
ever, also be used for the examination of regular biological 
preparations. 

If compared with the regular biological microscope, the 
polarization microscope is found characteristic of the following 
points: it is supplied with a polarization arrangement. The 
latter consists of a polarizer and analyzer. The polarizer is 
situated in a rotating mount beneath the condensing system. 

The microscope, of which the diagram is 
shown, possesses a triple "Ahrens" prism 
of calcite. The entering light is divided 
into two polarized parts, situated perpen- 
dicularly to each other. The so-called 
"ordinary" rays are reflected to one side 
by total reflection, which takes place on 
the inner cemented surface of the triple 
prism, allowing the so-called "'extra- 
ordinary" rays to pass through the con- 
denser. If the prism is adjusted to its 
focal point, it is so situated that the 
vibration plane of the extra-ordinary rays 
are in the same position as shown in 
Fig. 20.— Polarization the diagram of the illustration. 

Microscope The analyzer is mounted within the 

microscope-tube above the objective. 
Situated on a sliding plate, it can be shifted into the optical 
axis whenever necessary. The analyzer consists of a polari- 
zation prism after Glan-Thompson. The polarization plane 
of the active extraordinary rays is situated perpendicularly 
to the plane as shown in the diagram. The polarization 
prisms are ordinarily crossed. In this position the field of 
the microscope is darkened as long as no substance of a double 
refractive index has been introduced between the analyzer and 
polarizer. In rotating the polarizer up to the mark 90, the 
polarization prisms are mounted parallel and the field of the 




COMPOUND MICROSCOPES 



17 



microscope is lighted again. Immediately above the analyzer 
and attached to the mounting of the analyzer a lens of a com- 
paratively long focal length has been placed in order to over- 
come the difference in focus created by the introduction of the 
analyzer into the optical rays. 

The condensing system is mounted on a slider, and, further- 
more, can be raised and lowered along the optical centre by 
means of a rack-and-pinion adjustment. If lowered sufficiently, 
the condensing system can be thrown to the side to be removed 
from the optical rays. The condenser consists of three lenses. 
The two upper lenses are separately mounted to an arm, which 
permits them to be tilted to one side in order to be removed 
from the optical rays. The complete condenser is used only 
in connection with high-power objectives. As far as low-power 
objectives are concerned, the lower condensing lens alone is 
made use of, and the latter is found mounted to the polarizer 
sleeve. Below the polarizer and above the lower condensing 
lens an iris diaphragm is found. 

The microscope table is graduated on its periphery, and, 
furthermore, carries a vernier for more exact reading. 

The polarization microscope is not furnished with an ob- 
jective nose-piece. Every objective, however, is supplied with 
an mdividual centring head, which permits the objective to be 
attached to an objective clutch-changer, situated at the lower end 
of the microscope-tube. The centring head permits the objectives 
to be perfectly centred and to remain centred even if another 
objective is introduced into the objective clutch-changer. 

At an angle of 45 degrees to the polarization plane of polarizer 
and analyzer, a slot has been provided, which serves for the 
introduction of compensators. 

Between analyzer and ocular, another slot is found which 
permits the Amici-Bertrand lens to be introduced into the 
optical axis. The slider for the Bertrand lens is supplied with 
two centring screws whereby this lens can be perfectly and 
easily centred. The Bertrand lens serves the purpose of 
observing the back focal plane of the microscope objective. In 
order to allow the Bertrand lens to be focused, the tube can be 
raised and lowered for this purpose. An iris diaphragm is 
mounted above the Bertrand lens. 



IS 



HISTOLOGY OF MEDICINAL PLANTS 



If the Bertrand lens is shifted out of the optical axis, one can 
observe the preparation placed upon the microscope stage and, 
depending on its thickness or its double refraction, the inter- 
ference color of the specimen. This interference figure is called 
the orthoscopic image and, accordingly, one speaks of the micro- 
scope as being used as an "orthoscope." 

After the Bertrand lens has been introduced into the optical 
axis, the interference figure is visible in the back focal plane of 
the objective. Each point of this interference figure corresponds 
to a certain direction of the rays of the preparation itself. This 
arrangement permits observation of the change of the reflection 
of light taking place in the preparation, this in accordance with 
the change of the direction of the rays. This interference figure 
is called the conoscopic image, and, accordingly, the microscope 
is used as a "conoscope." 

Many types of polarization microscopes have been con- 
structed; those of a more elaborate form are used for research 
investigations; others of smaller design for routine investigations. 



CHAPTER III 



MICROSCOPIC MEASUREMENTS 

In making critical examinations of powdered drugs, it is 
frequently necessary to measure the elements under observation, 
particularly in the case of starches and crystals. 

OCULAR MICROMETER 

Microscopic measurements are made by the ocular microm- 
eter (Fig. 21). This consists of a circular piece of transparent 
glass on the centre of which is etched a one- or two-millimeter 
scale divided into one hundred or two hundred divisions re- 




FlG. 21. — Ocular Micrometer Fig. 22. — Stage Micrometer 

spectively. The value of each line is determined by standard- 
izing with a stage micrometer. 

STAGE MICROMETER 

The stage micrometer (Fig. 22) consists of a glass slide upon 
which is etched a millimeter scale divided into one hundred 
equal parts or lines: each line has a value of one hundredth of 
a millimeter. 

STANDARDIZATION OF OCULAR MICROMETER WITH LOW-POWER 

OBJECTIVE 

Having placed the ocular micrometer in the eye-piece and 
the stage micrometer on the centre of the stage, focus until 

19 



20 



HISTOLOGY OF MEDICINAL PLANTS 



the lines of the stage micrometer are clearly seen. Then adjust 
the scales until the lines of the stage micrometer are parallel 
with and directly under the lines of the ocular micrometer. 

Ascertain the number of lines of the stage micrometer covered 
by the one hundred lines of the ocular micrometer. Then 
calculate the value of each line of the ocular. This is done in 
the following manner: 

If the one hundred lines of the ocular cover seventy-five 
lines of the stage micrometer, then the one hundred lines of 
the ocular micrometer are equivalent to seventy-five one- 
hundredths, or three-fourths, of a millimeter. One line of the 
ocular micrometer will therefore be equivalent to one-hundredth 




Fig. 23. — Micrometer Eye-Piece 



of seventy-five one-hundredths, or .0075 part of a millimeter, 
and as a micron is the unit for measuring microscopic objects, 
this being equivalent to one one-thousandth of a millimeter, 
the value of each line of the ocular will therefore be 7.5 microns. 

With the high-power objective in place, ascertain the value 
of each line of the ocular. If one hundred lines of the ocular 
cover only twelve lines of the stage micrometer, then the one 
hundred lines of the ocular are equivalent to twelve one-hun- 
dredths of a millimeter, the value of one line being equivalent 
to one one-hundredth of twelve one-hundredths, or twelve ten- 
thousandths of a millimeter, or .0012, or 1.2 u. 

It will therefore be seen that objects as small as a thousandth 
of a millimeter can be accurately measured by the ocular 
micrometer. 

In making microscopic measurements it is only necessary 



MICROSCOPIC MEASUREMENTS 



21 



to find how many lines of the ocular scale are covered by the 
object. The number of lines multiplied by the equivalent of 
each line will be the size of the object in microns, or micro- 
millimeters. 

MICROMETER EYE-PIECES 

Micrometer eye-pieces (Figs. 23 and 24) may be used in 
making measurements. These eye-pieces with micrometer com- 




Fig. 24. — -Micrometer Eye-Piece 



binations are preferred by some workers, but the ocular microm- 
eter will meet the needs of the average worker. 

MECHANICAL STAGES 

Moving objects by hand is tiresome and unsatisfactory, first, 
because of the possibility of losing sight of the object under 
observation, and secondly, because the field cannot be covered 
so systematically as when a mechanical stage is used for moving 
slides. 

The mechanical stage (Fig. 25) is fastened to the stage by 
a screw. The slide is held by two clamps. There is a rack and 



22 



HISTOLOGY OF MEDICINAL PLANTS 



pinion for moving the slide to left or right, and another rack and 
pinion for moving the slide forward and backward. 



CAMERA LUCIDA 

The camera lucida is an optical mechanical device for aiding 
the worker in making drawings of microscopic objects. The 




Fig. 27. — Camera Lucida 



instrument is particularly necessary in research work where it 
is desirable to reproduce an object in all its details. In fact, all 
reproductions illustrating original work should be made by 
means of the camera lucida or by microphotography. 

A great many different types of camera lucidas or drawing 
apparatus are obtainable, varying from simple-inexpensive to 
complex-expensive forms. Figs. 26, 27, and 28 show simple 
and complex forms. 



24 



HISTOLOGY OF MEDICINAL PLANTS 



MICROPHOTOGRAPHIC APPARATUS 

The microphotographic apparatus (Fig. 29), as the name 
implies, is an apparatus constructed in such a manner that it 
may be attached to a microscope when we desire to photograph 
microscopic objects. It consists of a metal base and a polished 
metal pillar for holding the bellows, slide holder, ground-glass 
observation plate, and eye-piece. In making photographs, the 
small end of the bellows is attached to the ocular of the micro- 




FiG. 29. — Microphotographic Apparatus 



scope, the locus adjusted, and the object or objects photo- 
graphed. More uniform results are obtained in making such 
photographs if an artificial light of an unvarying candle-power 
is used. 

There are obtainable more elaborate microphotographic 
apparatus than the one figured and described, but for most 
workers this one will prove highly satisfactory. It is possible, 
by inclining the tube of the microscope, to make good micro- 
photographs with an ordinary plate camera. This is accom- 
plished by removing the lens of the camera and attaching the 
bellows to the ocular, focusing, and photographing. 



CHAPTER IV 



HOW TO USE THE MICROSCOPE 

In beginning work with the compound microscope, place 
the base of the microscope opposite your right shoulder, if you 
are right-handed; or opposite your left shoulder, if you are left- 
handed. Incline the body so that the ocular is on a level with 
your eye, if necessary; but if not, work with the body of the 
microscope in an erect position. In viewing the specimen, keep 
both eyes open. Use one eye for observation and the other 
for sketching. In this way it will not be necessary to remove 
the observation eye from the ocular unless it be to complete 
the details of a sketch. 

Learn to use both eyes. Most workers, however, accustom 
themselves to using one eye; when they are sketching, they use 
both eyes, although it is not necessary to do so. 

Open the iris diaphragm, and incline the mirror so that 
white light is reflected on the Abbe condenser. Place the slide 
on the centre of the stage, and if the slide contains a section 
of a plant, move the slide so as to place this specimen over the 
centre of the Abbe condenser. Then lower the body by means 
of the coarse adjustment until the low-power object, which 
should always be in position when work is begun, is within one- 
fourth of an inch of the stage. Then raise the body by means 
of the coarse adjustment until the object, or objects, in case a 
powder is being examined, is seen. Open and close the iris 
diaphragm, finally adjusting the opening so that the best pos- 
sible illumination is obtained for bringing out clearly the struc- 
ture of the object or objects viewed. Then regulate the focus 
by moving the body up or down by turning the fine adjustment. 
When studying cross-sections or large particles of powders, it 
is sometimes desirable to make low-power sketches of the speci- 
men. In most cases, however, only sufficient time should be 
spent in studying the specimen to give an idea of the size, struc- 

25 



26 



HISTOLOGY OF MEDICINAL PLANTS 



ture, and general arrangement or plan or structure if a section 
of a plant, or, if a powder, to note its striking characters. All 
the finer details of structure are best brought out with the 
high-power objective in position. 

In placing the high-power objective in position, it is first 
necessary to raise the body by the coarse adjustment; then 
open the iris diaphragm, and lower the body until the objective 
is within about one-eighth of an inch of the slide. Now raise 
the tube by the fine adjustment until the object is in focus, 
then gradually close the iris diaphragm until a clear definition 
of the object is obtained. Now proceed to make an accurate 
sketch of the object or objects being studied. 

In using the water or oil-immersion objectives it is first 
necessary to place a drop of distilled water or oil, as the case 
may be, immediately over the specimen, then lower the body 
by the coarse adjustment until the lens of the objective touches 
the water or the oil. Raise the tube, regulate the light by the 
iris diaphragm, and proceed as if the high-power objectives were 
in position. 

The water or oil should be removed from the obiectives and 
from the slide when not in use. 

After the higher-powered objective has been used, the body 
should be raised, and the low-power objective placed in position. 
If the draw-tube has been drawn out during the examination 
of the object, replace it, but be sure to hold one hand on the 
nose-piece so as to prevent scratching the objective and Abbe 
condenser by their coming in forceful contact. Lastly, clean 
the mirror with a soft piece of linen. In returning the micro- 
scope to its case, or to the shelf, grasp the limb, or the pillar, 
firmly and carry as nearly vertical as possible in order not to 
dislodge the eye-piece. 

ILLUMINATION 

The illumination for microscopic work may be from natural 
or artificial sources. 

It has been generally supposed that the best possible illumi- 
nation for microscopic work is diffused sunlight obtained from 
a northern direction. No matter from what direction diffused 



HOW TO USE THE MICROSCOPE 



27 



sunlight is obtained, it will be found suitable for microscopic 
work. In no case should direct sunlight be used, because it 
will be found blinding in its effects upon the eyes. Natural 
iUumination — diffused sunlight — varies so greatly during the 
different months of the year, and even during different periods 
of the day, that individual workers are resorting more and more 
to artificial illumination. The particular advantage of such 
illumination is due to the fact that its quality and intensity 
are uniform at all times. There are many ways of securing 
such artificial illumination, no one of which has any particular 
advantage over the other. Some workers use an ordinary gas 
or electric light with a color screen placed in the sub-stage 
below the iris diaphragm. In other cases a globe filled with a 
weak solution of copper sulphate is placed in such a way be- 
tween the source of light and the microscope that the light is 




Fig. 30. — [Micro Lamp 



focused on the mirror. Modern mechanical ingenuity has de- 
vised, however, a number of more convenient micro lamps 
(Fig. 30). These lamps are a combination of light and screen. 
In some forms a number of different screens come with each 
lamp, so that it is possible to obtain white-, blue-, or dark-ground 



28 



HISTOLOGY OF MEDICINAL PLANTS 



illumination. The type of the screen used will be varied accord- 
ing to the nature of the object studied. 

CARE OF THE MICROSCOPE 

If possible, the microscope should be stored in a room of 
the same temperature as that in which it is to be used. In 
any case, avoid storing in a room that is cooler than the place 
of use, because when it is brought into a warmer room, moisture 
will condense on the ocular objectives and mirrors. 

Before beginning work remove all moisture, dust, etc., from 
the inner and outer lenses of the ocular, the objectives, the 
Abbe condenser, and the mirror by means of a piece of soft, 
old linen. When the work is finished the optical parts should 
be thoroughly cleaned. 

If reagents have been used, be sure that none has got on 
the objectives or the Abbe condenser. If any reagent has got 
on these parts, wash it off with water, and then dry them thor- 
oughly with soft linen. 

The inner lenses of the eye-pieces and the under lens of the 
Abbe condenser should occasionally be cleaned. The mechani- 
cal parts of the stand should be cleaned if dust accumulates, and 
the movable surfaces should be oiled occasionally. Never 
attempt to make new combinations of the ocular or objective 
lenses, or transfer the objectives or ocular from one microscope 
to another, because the lenses of any given microscope form a 
perfect lens system, and this would not be the case if they were 
transferred. Keep clean cloths in a dust-proof box. Under no 
circumstances touch any of the optical parts with your fingers* 

PREPARATION OF SPECIMENS FOR CUTTING 

Most drug plants are supplied to pharmacists in a dried 
condition. It is necessary, therefore, to boil the drug in water, 
the time varying from a few minutes, in the case of thin leaves 
and herbs, up to a half hour if the drug is a thick root or woody 
stem. If a green (undried) drug is under examination, this 
first step is not necessary. 

If the specimen to be cut is a leaf, a flower-petal, or other 



HOW TO USE THE MICROSCOPE 



29 



thin, flexible part of a plant, it may be placed between pieces 
of elder pith or slices of carrot or potato before cutting. 

SHORT PARAFFIN PROCESS 

In most cases, however, more perfect sections will be ob- 
tained if the specimens are embedded in paraffin, by the quick 
paraffin process, which is easily carried out. 

After boiling the specimen in water, remove the excess of 
moisture from the outer surface with filter paper or wait until 
the water has evaporated. Next make a mould of stiff card- 
board and pour melted paraffin (melting at 50 or 60 degrees) 
into the mould to a height of about one-half inch, when the 
paraffin has solidified. This may be hastened by floating it 
on cool or iced water instead of allowing it to cool at room 
temperature. 

The specimens to be cut are now placed on the paraffin, 
with glue, if necessary, to hold them in position, and melted 
paraffin poured over the specimens until they are covered to a 
depth of about one-fourth of an inch. Cool on iced water, 
trim off the outer paraffin to the desired depth, and the speci- 
men will be in a condition suitable for cutting. 

Good workable sections may be cut from specimens embedded 
by this quick paraffin method. After a little practice the entire 
process can be carried out in less than an hour. This method 
of preparing specimens for cutting will meet every need of the 
pharmacognosist. 

LONG PARAFFIN PROCESS 

In order to bring out the structure of the protoplast (living 
part of the cell), it will be necessary to begin with the living 
part of the plant and to use the long paraffin method or the 
collodion method. 

Small fragments of a leaf, stem, or root-tip are placed in 
chromic-acid solution, acetic alcohol, picric acid, chromacetic 
acid, alcohol, etc., depending upon the nature of the specimen 
under observation. The object of placing the living specimen 
in such solutions is to kill the protoplast suddenly so that the 
parts of the cell will bear the same relationship to each other 



30 



HISTOLOGY OF MEDICINAL PLANTS 



that they did in the living plant, and to fix the parts so killed. 

After the fixing process is complete, the specimen is freed 
of the fixing agent by washing in water. From the water-bath 
the specimens are transferred successively to 10, 20, 40, 60, 70, 
80, 90, and finally 100 per cent alcohol. In this 100 per cent 
alcohol-bath the last traces of moisture are removed. The 




Fig. 31. — Paraffin-embedding Oven 



length of time required to leave the specimens in the different 
percentages of alcohols varies from a few minutes to twenty- 
four hours, depending upon the size and the nature of the 
specimen. 

After dehydration the specimen is placed in a clearing agent 
— chloroform or xylol — both of which are suitable when em- 
bedding in paraffin. The clearing agents replace the alcohol in 
the cells, and at the same time render the tissues transparent. 
From the clearing agent the specimen is placed in a weak solu- 
tion of paraffin, dissolved xylol, or chloroform. The strength of 
the paraffin solution is gradually increased until it consists 
of pure paraffin. The temperature of the paraffin-embedding 



HOW TO USE THE MICROSCOPE 



31 



oven (Fig. 31) should not be much higher than the melting- 
point of the paraffin. 

The specimen is now ready to be embedded. First make a 
mould of cardboard or a lead-embedding frame (Fig. 32), melt 
the paraffin, and then place the 
specimen in a manner that will 
facilitate cutting. Remove the 
excess of paraffin and cut when 
desired. 

In using the collodion method 
for embedding fibrous speci- Fig. 32.— Paraffin Blocks 
mens, as wood, bark, roots, etc., 

the specimen is first fixed with picric acid, washed with water, 
cleared in ether- alcohol, embedded successively in two, five, 
and twelve per cent ether-alcohol collodion solution, and finally 
embedded in a pure collodion bath. 

CUTTING SECTIONS 

Specimens prepared as described above may be cut with a 
hand microtome or a machine microtome. 

HAND MICROTOME 

In cutting sections by a hand microtome, it is necessary to 
place the specimen, embedded in paraffin or held between 
pieces of elder pith, carrot, or potato, over the second joints 
of the fingers, then press the first joints firmly upon the speci- 
men with the thumb pressed against it. If they are correctly 




Fig. 33. — Hand Microtome 



held, the specimens will be just above the level of the finger and 
the end of the thumb, and the joint will be below the level of 
the finger. 

Hold the section cutter (Fig. 33) firmly in the hand with 




32 



HISTOLOGY OF MEDICINAL PLANTS 



the flat surface next to the specimen. While cutting the sec- 
tion, press your arm firmly against your chest, and bend the 
wrist nearly at right angles to the arm. Push the cutting edge 
of the microtome toward the body and through the specimen 
in such a way as to secure as thin a section as possible. Do 
not expect to obtain nice, thin sections during the first or second 
trials, but continued practice will enable one to become quite 
efficient in cutting sections in this manner. 

When the examination of drugs is a daily occurrence, the 
above method will be found highly satisfactory. 

MACHINE MICROTOMES 

When a number of sections are to be prepared from a given 
specimen, it is desirable to cut the sections on a machine micro- 
tome, particularly when the sections are to be prepared for the 
use of students, in which case they should be as uniform as 
possible. 

Great care should be exercised in cutting sections with a 
machine microtome — first, in the selection of the type of the 
microtome; and secondly, in the style of knife used in cutting. 

For soft tissues embedded in paraffin or collodion, the rotary 
microtome with vertical knife will give best results. The thick- 
ness of the specimen is regulated by mechanical means, so that 
in cutting the sections it is only necessary to turn a crank and 
remove the specimens from the knife-edge, unless there is a 
ribbon-carrier attachment. If the sections are being cut from 
a specimen embedded by the quick paraffin method, it is best 
to drop the section in a metal cup partly filled with warm water. 
This will cause the paraffin to straighten out, and the specimen 
will uncoil. After sufficient specimens have been cut, the 
cup should be placed in a boiling-water bath until the paraffin 
surrounding the sections melts and floats on the water. Before 
removing the specimen from the water-bath, it is advisable to 
shake the glass vigorously in order to cause as many specimens 
as possible to settle to the bottom of the cup. The cup is then 
placed in iced water or set aside until the paraffin has solidified. 
The cake-like mass is then removed from the cup, and the sec- 
tions adhering to its under surface are removed by lifting them 
carefully off with the flat side of the knife and transferring them, 



HOW TO USE THE MICROSCOPE 



33 



together with the sections at the bottom of the cup, to a wide- 
mouth bottle, and covered with alcohol, glycerine, and water 
mixture; or if it is desired to stain the specimens, they should 
be placed in a weak alcoholic solution. 

Specimens having a hard, woody texture should be cut on 
a sliding microtome by means of a special wood knife, which 
is especially tempered to cut woody substances. Woody roots, 
wood, or thick bark may be cut readily on this microtome when 
they have been embedded by the quick paraffin process. The 
knife in the sliding microtome is placed in a horizontal position, 
slanting so that the knife-edge is drawn gradually across the 
specimen. After cutting, the sections are treated as described 
above. 

The thickness of the sections is regulated by mechanical 
means. After a section has been cut, the block containing the 
specimen is raised by turning a thumb-screw. In this microtome 
the knife, as in the rotary type, is fixed, and the block contain- 
ing the specimen is movable. 

If the specimen has been infiltrated with, and embedded in, 
paraffin or collodion, the treatment of the sections after cutting 
should be different. 

In the case of paraffin, the sections are fastened directly to 
the slide, and the paraffin is dissolved by either chloroform or 
xylol. The specimen is then placed in 100, 95, and 45 per cent 
alcohol, and then washed in water. These sections are now 
stained with water-stains, brought back through alcohol, cleared, 
and mounted in Canada balsam. 

If alcoholic stains are used, it will not be necessary to de- 
hydrate before staining, and the dehydration after staining will 
also be eliminated. 

Sections infiltrated with collodion are either stained directly 
without removing the collodion or after removal. 

FORMS OF MICROTOMES 

The hand cylinder microtome (Fig. 34) consists of a cylindrical 
body. The clamp for holding the specimen is near the top 
below the cutting surface. At the lower end is attached a microm- 
eter screw with a divided milled head. When moved forward 
one division, the specimen is raised 0.01 mm. This micrometer 



34 



HISTOLOGY OF MEDICINAL PLANTS 



screw has an upward movement of 10 mm. The cutting surface 
consists of a cylindrical glass ring. 

The hand table microtome (Fig. 35) is provided with a clamp, 
by which it may be attached to the edge of a table or desk. 




Fig. 34. — Hand Cylinder Microtome 

) 




Fig. 35. — Hand Table Microtome 



HOW TO USE THE MICROSCOPE 



35 



The cutting surface consists of two separated but parallel glass 
benches. The object is held by a clamp and is raised by a 
micrometer screw, which, when moved through one division by 
turning the divided head, raises the specimen o.oi mm. 

The sliding microtome has a track of 250 mm. The object 
is held by a clamp and its height regulated by hand. The disk 
regulating the micrometer screw is divided into one hundred 
parts. When this is turned through one division, the object is 
raised 0.005 min - or 5 microns, at the same time a clock-spring 
in contact with teeth registers by a clicking sound. If the disk 
is turned through two divisions, there will be two clicks, etc. 
In this way is regulated the thickness of the sections cut. When 
the micrometer screw has been turned through the one hundred 
divisions, it must be unscrewed, the specimen raised, and the 
steps of the process repeated. The knife is movable and is 
drawn across the specimen in making sections. 

The base sledge microtome (Fig. 36) has a heavy iron base 
which supports a sliding-way on which the object-carrier moves. 




Fig. 36. — Base Sledge Microtome 



The object-carrier is mounted on a solid mass of metal, and is 
provided with a clamp for holding the object. The object is 
raised by turning a knob which, when turned once, raises the 
specimen one to twenty microns, according to how the feeding 
mechanism is set. 



I 



36 



HISTOLOGY OF MEDICINAL PLANTS 



Sections thicker than twenty microns may be obtained by 
turning the knob two or more times. The knife is fixed and is 
supported by two pillars, the base of which may be moved for- 
ward or backward in such a manner that the knife can be 
arranged with an oblique or right-angled cutting surface. 

The minor rotary microtome (Fig. 37) has a fixed knife, held 
in position by two pillars, and a movable object-carrier. The 




Fig. 37. — Minor Rotary Microtome 



object is firmly secured by a clamp, and it is raised by a microm- 
eter screw. The screw is attached to a wheel having five 
hundred teeth on its periphery. A pawl is adjusted to the teeth 
in such a way that, when moved by turning a wheel to which 
it is attached, specimens varying from one to twenty-five microns 
in thickness may be cut, according to the way the adjusting disk 
is set. When the mechanism has been regulated and the object 
adjusted for cutting, it is only necessary to turn a crank in 
cutting sections. 

CARE OF MICROTOMES 

When not in use, microtomes should be protected from dust, 
and all parts liable to friction should be oiled. 



HOW TO USE THE MICROSCOPE 



37 



Microtome knives should be honed as often as is necessary 
to insure a proper cutting edge. After cutting objects, the 
knives should be removed, cleaned, and oiled. 

It should be kept clearly in mind that special knives are 
required for cutting collodion, paraffin, and frozen and woody 
sections. The cutting edges of the different knives vary con- 
siderably, as is shown in the preceding cuts. 



\ 



CHAPTER Y 
REAGENTS 

Little attention is given in the present work to micro-chemical 
reactions for the reason that their value has been much over- 
rated in the past. A few reagents will be found useful, however, 
and these few are given, as well as their special use. They are 
as follows : 

LIST OF REAGENTS 

Distilled Water. Is used in the alcohol, glycerine, and water 
mixture as a general mounting medium. It is used when warm 
as a test for inuhn and it is used in preparing various reagents. 

Glycerine. Is used in preparing the alcohol, glycerine, and 
water mixture, in testing for aleurone grains, and as a temporary 
mounting medium. 

Alcohol. Is used in preparing the alcohol , glycerine, and water 
mixture, in testing for volatile oils. 

Acetic Acid. Both dilute and strong solutions are used in 
testing for aleurone grains, cystoliths, and crystals of calcium 
oxalate. 

Hydrochloric Acid. Is used in connection with phloroglucin 
as a test for lignin and as a test for calcium oxalate. 

Ferric Chloride Solution. Is used as a test for tannin. 

Sulphuric Acid. Is used as a test for calcium oxalate. 

Tincture Alkana. Is used when freshly prepared by 
macerating the granulated root with alcohol and filtering, as a 
test for resin. 

Sodium Hydroxide. A five per cent solution is used as a 
test for suberin and as a clearing agent. 

Copper Ammonia. Is used as a test for cellulose. 

Ammonical Solution of Potash. Is used as a test for fixed 
oils. The solution is a mixture of equal parts of a saturated 
solution of potassium hydroxide and stronger ammonia. 

38 



REAGENTS 



39 



Oil of Cloves. Is used as a clearing fluid for sections pre- 
paratory to mounting in Canada balsam. 

Canada Balsam. Is used as a permanent mountmg medium 
for dehydrated specimens, and as a cement for ringing slides. 

Paraffin. Is used for general embedding and infiltrating. 

Lugol's Solution. Is used as a test for starch and for aleurone 
grains and proteid matters. 

Osmic Acid. A two per cent solution is used as a test for 
fixed oils. 

Alcohol, Glycerine, and Water Mixture. Is used as a tem- 
porary mounting medium and as a qualitative test for fixed oils. 

Chlorzinc Iodide. Is used as a test for suberin, lignin, cellu- 
lose and starch. 

Analine Chloride. Is used as a test for lignified cell walls of 
bast fibres and of stone cells. 

Phloroglucin. A one per cent alcoholic solution is used in 
connection with hydrochloric acid as a test for lignin. 

Haematoxylin-Delifields. Is used as a test for celluiose. 

REAGENT SET 

Each worker should be provided with a set of reagent bottles 
(Fig. 38), Such a set may be selected according to the taste 




Fig. 38. — Reagent Set 



of the individual, but experience has shown that a 30 c.c. bottle 
with a ground-in pipette and a rubber bulb is preferable to other 
types. In such forms the pipettes are readily cleaned, and the 
rubber bulbs can be replaced when they become old and brittle. 



40 



HISTOLOGY OF MEDICINAL PLANTS 



The entire set should be protected from dust by keeping it in a 
case, the cover of which should be closed when the set is not 
in use. 

MEASURING CYLINDER 

In order accurately to measure micro-chemical reagents, it 
is necessary to have a standard 50 ex. cylinder (Fig. 39) graduated 




Fig. 39. — Measuring Cylinder Fig. 40. — Staining Dish 

to c.c.'s. Such a cylinder should form a part of the reagent set. 

STAINING DISHES 

There is a great variety of staining dishes (Fig. 40), but 
for general histological work a glass staining dish with groves 
for holding six or more slides and a glass cover is most desirable. 



CHAPTER VI 



HOW TO MOUNT SPECIMENS 

The method of procedure in mounting specimens for study 
varies according to the nature of the specimen, its preliminary 
treatment, and the character of the mount to be made. As to 
duration, mounts are either temporary or permanent. 

TEMPORARY MOUNTS 

In preparing a temporary mount, place the specimen in the 
centre of a clean slide and add two or more drops of the tem- 
porary mounting medium, which may be water, or a mixture 
of equal parts of alcohol, glycerine, and water, or some micro- 
chemical reagent, as weak Lugol's solution, solution of chloral 
hydrate, etc. Cover this with a cover glass and press down 
gently. Remove the excess of the mounting medium with a 
piece of blotting paper. Now place the slide on the stage and 
proceed to examine it. Such mounts can of course be used only 
for short periods of study; and when the period of observation 
is finished, the specimen should be removed and the slide washed, 
or the slide washing may be deferred until a number of such 
slides have accumulated. At any rate, when the mounting 
medium dries, the specimen is no longer suitable for observation. 

PERMANENT MOUNTS 

Permanent mounts are prepared in much the same way as 
temporary, but of course the mounting medium is different. 
The kind of permanent mounting medium used depends upon 
the previous treatment of the specimen. If the specimen has 
been preserved in alcohol or glycerine and water, it is usually 
mounted in glycerine jelly. If the specimen in question is a 
powder, it is placed in the centre of the slide and a drop or two 

41 



42 



HISTOLOGY OF MEDICINAL PLANTS 



of glycerine, alcohol, and water mixture added, unless the 
powder was already in suspension in such a mixture. Cut a 
small cube of glycerine jelly and place it in the centre of the 
powder mixture. Lift up the slide by means of pliers, or grasp 
the two edges between the thumb and ringer and hold over a 
small flame of an alcohol lamp, or place on a steam-bath until 
the glycerine jelly has melted. Next sterilize a dissecting needle, 
cool, and mix the powder with the glycerine jelly, being careful 
not to lift the point of the needle from the slide during the 
operation. If the mixing has been carefully done, few or no 
air-bubbles will be present; but if they are present, heat the 
needle, and while it is white hot touch the bubbles with its 
point, and they will disappear. Now take a pair of forceps and, 
after securing a clean cover glass near the edge, pass them three 
times through the flame of the alcohol lamp. While holding it 
in a slanting position, touch one side of the powder mixture and 
slowly lower the cover glass until it comes in complete contact 
with the mixture. Now press gently with the end of the needle- 
handle, and set it aside to cool. When it is cool, place a neatly 
trimmed label on one end of the slide, on which write the name 
of the specimen, the number of the series of which it is to form 
a part, etc. Any excess of glycerine jelly, which may have 
been pressed out from the edges of the cover glass, should not 
be removed at once, but should be allowed to remain on the 
slide for at least one month in order to allow for shrinkage due 
to evaporation. At the end of a month remove the glycerine 
jelly by first passing the blade of a knife, held in a vertical 
position, the back of the knife being next to the slide, around 
the edge of the cover glass. After turning the knife-blade so 
that the flat side is in contact with slide, remove the jelly outside 
of the cover glass. Any remaining fragments should be removed 
with a piece of old linen or cotton cloth. Finally, ring the edge 
of the cover glass with microscopical cement, of which there 
are many types to be had. If the cleaning has been done 
thoroughly, there is no better ringing cement than Canada 
balsam. 

In mounting cross-sections, the method of procedure is 
similar to the above, with the exception that the glycerine jelly 
is placed at the side of the specimen and not in the centre. 



HOW TO MOUNT SPECIMENS 



43 



While melting the jelly, incline the slide in order to allow the 
melted glycerine jelly to flow gradually over the specimen, thus 
replacing the air contained in the cells and intercellular spaces. 
Finish the mounting as directed above, but under no conditions 
should you stir the glycerine jelly with the section. 

If specimens, after having been embedded in paraffin or 
collodion, are cut, cleared, stained, and dehydrated, they are 
usually mounted in Canada balsam. A small drop of this sub- 
stance, which may be obtained in collapsible tubes, is placed 
at one side of the specimen. While inclining the slide, gently 
heat until the Canada balsam covers the specimen. Secure a 
cover glass by the aid of pliers, pass it through the flame three 
times, and lower it slowly while holding it in an inclined position. 
Press gently on the cover glass with the needle-handle, and keep 
in a horizontal position for twenty-four hours, then place directly 
in a slide box or cabinet, since no sealing is required. 

Glycerine is sometimes used to make permanent mounts, but 
it is unsatisfactory, because the cover glass is easily removed 
and the specimen spoiled or lost, unless ringed — a procedure 
which is not easily accomplished. If the specimen is to be 
mounted in glycerine, it must first be placed in a mixture of 
alcohol, glycerine, and water, and then transferred to glycerine. 
Lactic acid is another permanent liquid-mounting medium, 
which is unsatisfactory in the same way as glycerine, but like 
glycerine, there are certain special cases where it is desirable 
to use it. When this is used, the slides should be kept in a 
horizontal position, unless ringed. 

COVER GLASSES 

Great care should be used in the selection of cover glasses, 
however, not only as regards their shape but as to their thickness. 
The standard tube length of the different manufacturers makes 
an allowance of a definite thickness for cover glasses. It is 
necessary, therefore, to use cover glasses made by the manu- 
facturer of the microscope in use. 

Cover glasses are either square or round. Of each there are 
four different thicknesses and two different sizes. The standard 
thicknesses are: 



44 



HISTOLOGY OF MEDICINAL PLANTS 



The small size is designated three-fourths and the large 
size seven-eighths. 

Cover glasses are circular (Fig. 41), square (Fig. 42), or 
rectangular (Fig. 43) pieces of transparent glass used in covering 
the specimens mounted on glass slides. A few years ago much 
difficulty was experienced in obtaining uniformly thick and 




Fig. 41. — Round Fig. 42. — Square Fig. 43. — Rectangular Cover 

Cover Glass Cover Glass Glass 

transparent cover glasses, but no such difficulty is experienced 
to-day. The type of cover glass used depends largely upon the 
character of the specimen to be mounted. The square and 
rectangular glasses are selected when a series of specimens are 
to be mounted, but in mounting powdered drugs and histological 
specimens the round cover glasses are preferable because they 
are more sightly and more readily cleaned and rinsed. 

GLASS SLIDES 

Glass slides (Fig. 44) are rectangular pieces of transparent 
glass used as a mounting surface for microscopic objects. The 




Fig. 44. — Glass Slide 



slides are usually three inches long by one inch wide, and they 
should be composed of white glass, and they should have ground 



HOW TO MOUNT SPECIMENS 



45 



and beveled edges. Slides should be of uniform thickness, and 
they should not become cloudy upon standing 

SLIDE AND COVER-GLASS FORCEPS 

Slides and cover glasses should be grasped by their edges. 
To the beginner this is not easy. In order to facilitate holding 
slides and cover glasses during the mounting process, one may 
use a slide and a cover-glass forceps. The slide forceps consists 
of wire bent and twisted in such a way that it holds a slide 
firmly when attached to its two edges. 

There are various forms of cover-glass holders, but only two 
types as far as the method of securing the cover glass is con- 




FlG. 45. — Histological Forceps 

cerned. First, there are the bacteriological and the histological 
forceps (Fig. 45), which are self-closing. The two blades of such 
forceps must be forced apart by pressure in securing the cover 
glass. The second type of forceps is that in which the two 
blades are normally separated (Fig. 46), it being necessary to 




Fig. 46. — Forceps 

press the blades to either side of the cover glass in order to 
secure and hold it. There is a modification of this type of 




forceps which enables one to lock the blades by means of a slid- 
ing pin (Fig. 47), after the cover glass has been secured. It is 



46 HISTOLOGY OF MEDICINAL PLANTS 

well to accustom oneself to one type, for by so doing one may 
become dexterous in its use. 

NEEDLES 

Two dissecting needles (Fig. 48) should form a part of the 
histologist's mounting set. The handles mav be of any material, 



Fig. 48. — Dissecting Needle 

but the needle should be of tempered steel and about two inches 
long. 

SCISSORS 

Almost any sort of scissors (Fig. 49) will do for histology 
work, but a small scissors with fine pointed blades, are preferred. 




Fig. 49. — Scissors 



Scissors are useful in trimming labels and in cutting strips of 
leaves and sections of fibrous roots that are to be embedded 
and cut. 

SCALPELS 

Scalpels (Fig. 50) have steel blades and ebony handles. 
These vary in regard to size and quality of material. The 
cheaper grades are quite as satisfactory, however, as the more 
expensive ones, and for general use a medium-sized blade and 
handle will be found most useful. 

TURNTABLE 

Much time and energy may be saved by ringing slides on a 
turntable (Fig. 51). There is a flat surface upon which to rest 
the hand holding the brush with cement, and a revolving table 



HOW TO MOUNT SPECIMENS 47 

upon which the slide to be ringed is held by means of two clips. 
In ringing slides, it is only necessary to revolve the table, and 




Fig. 51. — Turntable 

at the same time to transfer the cement to the edge of the 
cover glass from the brush held in the hand. 

LABELING 

There are many ways of labeling slides, but the best method 
is to place on the label the name of the specimen, the powder 



48 



HISTOLOGY OF MEDICINAL PLANTS 



number, and the box, the tray or cabinet number. For 
example : 

Powdered Arnica Flowers 
No. 80 — Box A — 600. 

PRESERVATION OF MOUNTED SPECIMENS 

Accurately mounted, labeled, and ringed slides should be 
filed away for future study and reference. Such filing may 




Fig. 52. — Slide Box 




Fig. 53. — Slide Tray 



be done in slide boxes, in slide trays, or in cabinets. Slide 
boxes are to be had of a holding capacity varying from one to 



HOW TO MOUNT SPECIMENS 



49 



one hundred slides. For general use, slide boxes (Fig. 52) hold- 
ing one hundred slides will be found most useful. Some workers 
prefer trays (Fig. 53), because of the saving of time in selecting 
specimens. Trays hold twenty slides arranged in two rows. 
The cover of the tray is divided into two sections so that, if 




Fig. 54. — Slide Cabinet 



desired, only one row of slides is uncovered at a time. Slide 
cabinets (Fig. 54) are particularly desirable for storing large 
individual collections, particularly when the slides are used 
frequently for reference. Large selections of slides should be 
numbered and card indexed in order to facilitate finding. 



Part II 

TISSUES CELLS, AND CELL CONTENTS 



CHAPTER I 



THE CELL 

The cell is the unit of structure of all plants. In fact the 
cell is the plant in many of the lower forms — so called unicellular 
plants. All plants, then, consist of one or more cells. 

While cells vary greatly in size, form, color, contents, and 
function, still in certain respects their structure is identical. 

TYPICAL CELL 

The typical vegetable cell is composed of a living portion or 
protoplast and an external covering, or wall. The protoplast in- 
cludes everything within the wall. It is made up of a number 
of parts, each part performing certain functions yet harmonizing 
with the work of the cell as a whole. The protoplast (proto- 
plasm) is a viscid substance resembling the white of an egg. 
The protoplast, when unstained and unmagnified, appears 
structureless, but when stained with dyes and magnified, it is 
found to be highly organized. The two most striking parts of 
the protoplast are the cytoplasm and the nucleus. The part 
of the protoplast lining the innermost part of the wall is the 
ectoplast, which is less granular and slightly denser than most 
of the cytoplasm. The cytoplasm is decidedly granular in 
structure. 

In the cytoplasm occurs one or more cavities, vacuoles, rilled 
with cell sap. Embedded in the cytoplasm are numerous 
chromatophores, which vary in color in the different cells, from 
colorless to yellow, to red, and to green. The nucleus is the 
seat of the vital activity of the cell, and the seat of heredity. 
The whole life and activity of the cell centre, therefore, in and 
about the nucleus. 

The outer portion of the nucelus consists of a thin membrane 
or wall. The membrane encloses numerous granular particles — 

53 



54 



HISTOLOGY OF MEDICINAL PLANTS 



chromatin — which are highly susceptible to organic stains. 
Among the granules are thread-like particles or linin. Near 
the centre of the nucelus are one or more small rounded nucleoli. 
The liquid portion of the nucleus, rilling the membranes and 
surrounding the chromatin, linin, and nucleoli, is the nuclear 
sap. 

Other cell contents characteristic of certain cells are crystals, 
starch, aleurone, oil, and alkaloids. The detailed discussion of 
these substances will be deferred until a later chapter. 

The cell wall which surrounds the protoplast is a product of 
its activity. The structure and composition of the wall of any 
given cell vary according to the ultimate function of the cell. 
The walls may be thin or thick, porous or non-porous, and 
colored or colorless. The composition of cell walls varies greatly. 
The majority of cell walls are composed of cellulose, in other 
cells of linin, in others of cutin, and in still others of suberin, etc. 
In the majority of cells the walls are laid down in a series of 
layers one over the other by apposition, similar to the manner 
of building a pile of paper from separate sheets. The first layer 
is deposited over the primary wall, formed during cell division; 
to this is added another layer, etc. A modification of this 
manner of growth is that in which the layers are built up one 
over the other, but the building is gradually done by the deposit 
of minute particles of cell- wall substance over the older de- 
posits. Such walls are never striated, as is likely to be the case 
in cell walls formed by the first method. In other cells the walls 
are increased in thickness by the deposition of new wall material 
in the older membrane. The cell walls will be discussed more 
fully when the different tissues are studied in detail. 

INDIRECT CELL DIVISION (kARYOKINESIS) 

The purpose of cell division is to increase the number of cells 
of a tissue, an organ, an organism, or to increase the number of 
organisms, etc. Such cell divisions involve, first, an equal 
division of the protoplast and, secondly, the formation of a wall 
between the divided protoplasts. The first changes in structure 
of a cell undergoing division occur in the nucleus. 



THE CELL 



55 



CHANGES IN A CELL UNDERGOING DIVISION 

The linin threads become thicker and shorter. The chro- 
matin granules increase in size and amount; the threads and 
chromatin granules separate into a definite number of segments 
or chromosomes (Plate i, Fig. 2). The nuclear membrane be- 
comes invested with a fibrous protoplasmic layer which later 
separates and passes into either end of the cell, there forming 
the polar caps (Plate 1, Fig. 3). 

The nuclear membrane and the nucleoli disappear at about 
this time. Two fibres, one from each polar cap, become at- 
tached to opposite sides of the individual chromosomes. Other 
fibres from the two polar caps unite to form the spindle fibres, 
which thus extend from pole to pole. All these spindle fibres 
form the nuclear spindle (Plate 1, Fig. 5). 

The chromosomes now pass toward the division centre of 
the cell or equatorial plane and form, collectively, the equatorial 
plate (Plate 1, Fig. 5). At this point of cell division, the chromo- 
somes are U-shaped, and the curved part of the chromosomes 
faces the equatorial plane. The chromosomes finally split into 
two equal parts (Plate 1, Fig. 6). The actual separation of the 
halves of chromosomes is brought about by the attached polar 
fibres, which contract toward the polar caps (Plate 1, Fig. 7). 
The chromosomes are finally drawn to the polar caps (Plate 1, 
Fig. 8). The chromosomes now form a rounded mass. They 
then separate into Hnin threads and chromatin granules. Nuc- 
leoli reappear, and nuclear sap forms. Finally, a nuclear mem- 
brane develops. The spindle fibres, which still extend from 
pole to pole, become thickened at the equatorial plane (Plate 1, 
Fig. 8), and finally their edges become united to form the cell- 
plate (Plate 1, Fig. 9), which extends across the cell, thus com- 
pletely separating the mother cell into two daughter cells. After 
the formation of the cell-plate, the spindle fibres disappear. 
The cell becomes modified to form the middle lamella, on either 
side of which the daughter protoplast adds a cellulose layer. 
The ultimate composition of the middle lamella and the com- 
position and structure of the cell wall will differ according to 
the function which the cell will finally perform. 



PLATE i 




THE CELL 



57 



ORIGIN OF MULTICELLULAR PLANTS 

All multicellular plants are built up by the repeated cell 
division of one original cell. If the cells formed are similar in 
structure and function, they form a tissue. In multicellular 
plants many different kinds of tissues will be formed as a result 
of cell division, since there are many different functions to be 
performed by such an organism. When several of these tissues 
become associated and their functions are correlated, they form 
an organ. The association of several organs in one form makes 
an organism. The oak-tree is an organism. It is made up of 
organs known as flowers, leaves, stems, roots, etc. Each of 
these organs is in turn made up of several kinds of tissue. In 
some cases it is difficult to designate a single function to an 
aggregation of cells (tissue). In fact, a tissue may perform 
different functions at different periods of its existence or it 
may perform two functions at one and the same time; as an 
example, stone cells, whose primary function is mechanical, in 
many cases function as storage tissue. The cells forming the 
tissues of the plant, in fact, show great adaptability in regard 
to the function which they perform. Nevertheless there is a 
predominating function which all tissues perform, and the 
structure of the cells forming such tissues is so uniform that it 
is possible to classify them. 

The functional classification of tissues is chosen for the 
purpose of demonstrating the adaptation of cell structure to 
cell function. If the cells performing a similar function in the 
different plants were identical in number, distribution, form, 
color, size, structure, and cell contents, there would not be a 
science of histology upon which the art of microscopic pharma- 
cognosy is based. It may be said, however, with certainty, 
that the cells forming certain of the tissues of any given species 
of plant will differ in a recognizable degree from cells perform- 
ing a similar function in other species of plants. Often a tissue 
is present in one plant but absent in another. For example, 
many aquatic plants are devoid of mechanical fibrous cells. 
The barks of certain plants have characteristic stone cells, while 
in many other barks no stone cells occur. Many leaves have 
characteristic trichomes; others are free from trichomes, etc. 



58 



HISTOLOGY OF MEDICINAL PLANTS 



Yet all cells performing a given function will structurally re- 
semble each other. In the present work the nucleus and other 
parts of the living protoplast will not be considered, for the 
reason that these parts are not in a condition suitable for study, 
because most drugs come to market in a dried condition, a con- 
dition which eliminates the possibility of studying the proto- 
plast. The general structure of the cells forming the different 
tissues will first be considered, then their variation, as seen in 
different plants, and finally their functions. 



CHAPTER II 



THE EPIDERMIS AND PERIDERM 

The epidermis and its modifications, the hypodermis and 
the periderm, form the dermal or protective outer layer or layers 
of the plant. 

The epidermis of most leaves, stems of herbs, seeds, fruits, 
floral organs, and young woody stems consists of a single layer 
of cells which form an impervious outer covering, with the 
exception of the stoma. 

LEAF EPIDERMIS 

The cells of the epidermis vary in size, in thickness of the 
side and end walls, in form, in arrangement, in character of 
outgrowths, in the nature of the surface deposits, in the char- 
acter of wall — whether smooth or rough — and in size. 

In cross-sections of the leaf the character of both the side 
and end walls is easily studied. 

In surface sections — the view most frequently seen in pow- 
ders — the side walls are more conspicuous than the end wall 
(Plates 2 and 3). This is so because the light is considerably re- 
tarded in passing through the entire length of the side walls, 
while the light is retarded only slightly in passing through the 
end wall. The light in this case passes through the width 
(thickness) of the wall only. The outer walls of epidermal cells 
are characteristic only when they are striated, rough, pitted, 
colored, etc. In the majority of leaves the outer wall of the 
epidermal cells is not diagnostic in powders, or in surface 
sections. 

The thickness of the end and side walls of epidermal cells 
differs greatly in different plants. 

As a rule, leaves of aquatic and shade-loving plants, as well 
as the leaves of most herbs have thinner walled epidermal cells 

59 



PLATE 2 




Leaf Epidermis 

1. Uva-ursi (Arctostaphylos uva-ursi, [L.] Spring). 

2. Boldus (Peumus boldus, Molina). 

3. Catnip (Nepeta cataria, L.). 

4. Digitalis (Digitalis purpurea, L.). 
4-A. Origin of hair. 



PLATE 3 




Leaf Epidermis 



1. Upper striated epidermis of chirata leaf (Swertia chirata, [Roxb.] Ham.). 

2. Green hellebore leaf (Veratrum viride, Ait.). 

3. Boldus leaf (Peumus boldus, Molina). 

4. Under epidermis of India senna (Cassia angustifolia, Vahl.). 



62 



HISTOLOGY OF MEDICINAL PLANTS 



than have the leaves of plants growing in soil under normal 
conditions, or than have the leaves of shrubs and trees. 

The widest possible range of cell-wall thickness is therefore 
found in the medicinal leaves, because the medicinal leaves are 
collected from aquatic plants, herbs, shrubs, trees, etc. 

The outer wall is always thicker than the side walls. Even 
the side walls van- in thickness in some leaves, the waU next 
to the epidermis being thicker than the lower or innermost 
portion of the wall. Frequent!}- the outermost part of the side 
walls is unequally thickened. This is the case in the beaded 
side walls characteristic of the epidermis of the leaves of laurus, 
myrcia. boldus. and capsicum seed. etc. The thickness of the 
side walls of the epidermal cells of most leaves varies in the 
different leaves. 

In most leaves there are five typical forms of arrangement of 
epidermal calls: First, those over the veins which are elongated 
in the direction of the length of the leaf; and. secondly, those 
on other parts of the leaf which are usually several-sided and 
not elongated in any one direction. If the epidermis of the leaf 
has stoma, then there is a third type of arrangement of the 
epidermal cells around the stoma; fourthly, the cells surrounding 
the base of hairs; and fifthly, outgrowths of the epidermis, 
non-glandular and glandular hairs, etc. 

It should be borne in mind that in each species of plant the 
five types of arrangement are characteristic for the species. 

The character of the outer wall of the epidermal cells differs 
greatly in different plants. In most cases the wall is smooth; 
senna is an example of such leaves. In certain other leaves the 
wall is rough, the roughness being in the form of striatioiis. 
In some cases the striatioiis occur in a regular manner; bella- 
donna leaf is typical of such leaves. In other instances the wall 
is striated in an irregular manner as shown hi cliirata epidermis. 
Very often an epidermis is rough, but the roughness is not due 
to striatioiis. In these cases the epidermis is unevenly thickened, 
the thin places appearing as slight depressions, the thick places 
&s slight elevations. Boldus has a rough, but not a striated 
surface. 

Surface deposits are not of common occurrence in medicinal 
plants; waxy deposits occur on the stem of sumac, on a species 



THE EPIDERMIS AXD PERIDERM 



63 



of raspberry, on the fruit of bayberry, etc. Resinous deposits 
occur on the leaves and stems of grindelia species, and on yerba 
santa. 

In certain leaves there are two or three layers of cells beneath 
the epidermis that are similar in structure to the epidermal cells. 
These are called hypodermal cells, and they function in the 
same way as the epidermal cells. 

Hypodermal cells are very likely to occur on the margin of 
the leaf. Uva-ursi leaf has a structure typical of leaves with 
hypodermal marginal cells. Uva-ursi. like other leaves with 
hypodermal cells has a greater number of hypodermal cells 
at the leaf margin than at any other part of the leaf 
surface. 

The cutinized walls of epidermal cells are stained red with 
saffranin. 

TESTA EPIDERMIS 

Testa epidermal cells form the epidermal layers of such 
seeds as lobelia, henbane, capsicum, paprika, larkspur, bella- 
donna, scopola. etc. 

In surface view the end walls are thick and wavy in outline; 
frequently the line of union — middle lamella — of two cells is in- 
dicated by a dark or light line, while in others the waU between 
two cells appears as a single wall. The walls are porous or 
non-porous, and the color of the wall varies from yellow to 
brown, to colorless. These cells always occur in masses, com- 
posed partially of entire and partially of broken fragments. 

In lobelia seed (Plate 4. Fig. 2) the line of union of adjacent 
ceU walls appears as a dark line. The walls are wavy in out- 
line, of a yellowish-red color and not porous. 

In henbane seed I Plate 4. Fig. 3) the line of union between 
the cells is scarcely visible; the walls are decidedly wavy, more 
so than in lobelia, and no pits are visible. 

In capsicum seed 1 Plate 4. Fig. 1) the cells are very wavy 
and decidedly porous, the line of union between the cell walls 
being marked with irregular spaces and lines. 

In belladonna seed ('Plate 5. Fig. 1) the walls between two 
adjacent cells are non-striated and non-porous, and extremely 
irregular in outline. 



PLATE 4 




Testa Epidermal Cells 



1. Capsicum seed {Capsicum frutescens, L.). 

2. Lobelia seed (Lobelia inflata, L.). 

3. Henbane seed (Hyoscyamus niger, L.). 



PLATE 5 




66 



HISTOLOGY OF MEDICINAL PLANTS 



In star-anise seed (Plate 5, Fig. 2) the walls are irregularly 
thickened and wavy in outline. 

In stramonium seed (Plate 5, Fig. 3) the walls are very 
thick, wavy in outline, and striated. 

PLANT HAIRS (trichomes) 

In histological work plant hairs are of great importance, as 
they offer a ready means of distinguishing and differentiating 
between plants, or parts of plants, when they occur in a broken 
or finely powdered condition. There is no other element in 
powdered drugs which is of so great a diagnostic value as the 
plant hair. The same plant will always have the same type 
of hair, the only noticeable variation being in the size. In 
microscopical drug analysis the presence of hairs is always noted, 
and in many cases the purity of the powder can be ascertained 
from the hairs. Botanists seem to have given little attention to 
the study of plant hairs. This accounts for the fact that in- 
formation concerning them is very meagre in botanical literature, 
and, as far as the author can learn, no one has attempted to 
classify them. In systematic work, plant hairs could be used 
to great advantage in separating genera and even species. 
Hairs are, of course, a factor now in systematic work. The 
lack of hairs is indicated by the term glabrous. Their presence 
is indicated by such terms as hispid, villous, etc. In certain 
cases the term indicates position of the hair as ciliate when the 
hair is marginal. When hairs influence the color of the leaf, 
such terms as cinerous and canescent are used. In all the cases 
cited no mention is made of the real nature of the hair. 

In systematic work, as in pharmacognosy, we must work 
with dried material, and it is only those hairs which retain 
their form under such conditions which are of classification 
value. 

Hairs are the most common outgrowths of the epidermal 
cells. They are classified as glandular or non-glandular, accord- 
ing to their structure and function. The glandular hairs will 
be considered under synthetic tissue. 

Each group is again subdivided into a number of secondary 
groups, depending upon the number of cells present, their form,, 



THE EPIDERMIS AND PERIDERM 



67 



their arrangement, their size, their color, the character of their 
walls, whether rough or smooth, whether branched or non- 
branched, whether curved, twisted, straight, or twisted and 
straight, whether pointed, blunt, or forked. 

FORMS OF HAIRS 

PAPILLA 

Papillae are epidermal cells which are extended outward in 
the form of small tubular outgrowths. 

Papillae occur on the following parts of the plant: flower- 
petals, stigmas, styles, leaves, stems, seeds, and fruits. Papillae 
occur on only a few of the medicinal leaves. 

The under surface of both Truxillo (Plate 6, Fig. 3) and 
Huanuca coca have very small papillae. The outermost wall of 
these papillae are much thicker than the side walls. The papillae 
of klip buchu (Plate 6, Fig. 4), an adulterant of true buchu, has 
large thick- walled papillae. 

The velvety appearance of most flower-petals (Plate 6, 
Figs. 2 and 5) is due to the presence of papillae. The papillae 
of flower-petals are very variable. In calendula flowers (Plate 
6, Fig. 1) they are small, yellowish in color, and the outer wall 
is marked with parallel striations which appear as small teeth 
in cross-section. The ray petal papillae of anthemis consist of 
rather large, broad, blunt papillae with slightly striated walls. 
The papillae of the ray petals of the white daisy consist of papillae 
which have medium sized, cone-shaped papillae with finely striated 
walls. The papillae of the flower stigma vary greatly in different 
flowers. In some cases two or more types of papillae occur, 
but even in these cases the papillae are characteristic of the 
species. 

The papillae differ greatly in the case of the flowers of the 
compositae, where two types of flowers are normally present — 
namely, the ray flowers and the disk flowers. 

In all cases observed the papillae of the stigma of the ray 
flowers are always smaller than the papillae of the stigma of the 
disk flowers. It would appear from extended observation that 
the papillae of the ray flower stigma are being gradually aborted. 
The papillae of the style are always different from the papillae 



PLATE 6 




Papillae 

1. Calendula flowers {Calendula officinalis, L.). 

2. White daisy ray flower (Chrysanthemum leucanthemum , L.). 

3. Coca leaf (Eryihroxylon coca, Lamarck). 

4. Klip buchu. 

.5. Anthemis ray petal (Anthemis nobilis, L.). 



THE EPIDERMIS AND PERIDERM 



69 



of the stigma. The style papillae are always smaller, and they 
are of a different form. 

UNICELLULAR NON-GLANDULAR HAIRS 

True plant hairs are tubular outgrowths of the epidermal 
cell, the length of these outgrowths being several tim.es the 
width of the hair. 

The unicellular hairs are common to many plants. The two 
groups of non-glandular unicellular hairs are, first, the solitary; 
and secondly, the clustered hairs. 

Solitary unicellular hairs occur on the leaves of chestnut, 
verba santa, lobelia, cannabis indica, the fruit of anise, and 
the stem of allspice, senna, and cowage. 

Chestnut hairs (Plate 7, Fig. 1) have smooth yellowish-colored 
walls, and the cell cavity contains reddish-brown tannin. These 
hairs occur solitary or clustered; the clustered hairs normally 
occur on the leaf , but in powdering the drug, individual hairs of 
the cluster become separated or solitary. 

Yerba santa hairs (Plate 7, Fig. 4) are twisted, the lumen or 
cell cavity is very small, and the walls, which are very thick, 
are grayish- white. 

Lobelia hairs (Plate 7, Fig. 5) are very large. The walls 
are grayish- white, and the outer surface extends in the form 
of small elevations which make the hair very rough. The hair 
tapers gradually to a solid point. 

Cannabis indica hairs (Plate 7, Fig. 6) are curved. The 
apex tapers to a point and the base is broad, and it frequently 
contains deposits of calcium carbonate. The walls are grayish- 
white in appearance, and rough. The roughness increases 
toward the apex. 

The hairs of the anise (Plate 7, Fig. 7) are mostly curved; 
the walls are thick, yellowish- white, and the outer surface is 
rough; this is due to the numerous slight centrifugal projections 
of the outer wall. 

Allspice stem hairs (Plate 7, Fig. 2) have smooth walls. 
The cell cavity is reddish-brown. The hair is curved. 

The hair of senna (Plate 7, Fig. 10) is light greenish-yellow 
with rough papillose walls. The hair is usually curved and 
tapering, and it does not have any characteristic cell contents. 



PLATE 7 




Unicellular Solitary Hairs 

1. Chestnut leaf (Castanea dentata, [Marsh] Borkh). 

2. Allspice stems (Pimento, officinalis, Lindl.). 

3. Cowage. 

4. Yerba santa (Eriodictyon calif ornicum, [H. and A.] Greene). 

5. Lobelia (Lobelia inflata, L.). 

6. Cannabis indica (Cannabis sativa, L.). 

7. Anise fruit (Pimpinella anisum, L.). 

8. Hesperis matronalis (Hesperis matronalis, L.). 

9. Galphimia glauca (Galphimia glauca, Cav.). 
10. Senna (Cassia angustifclia, Vahl.). 



PLATE 8 




Clustered Unicellular Hairs 
i and 2. European oak {Quercus injector ia, Olivier). 

3. Kamala {MaUotus philippinensis, [Lam.] [Muell.] Arg.). 

4. Witch-hazel leaf {Hamamelis virginiana, L.). 

5. Althea leaf (Althcea officinalis, L.). 



72 



HISTOLOGY OF MEDICINAL PLANTS 



Cowage hairs (Plate 7, Fig. 3) are lance-shaped, and they 
terminate in a sharp point. The outer wall contains numerous 
recurved teeth-like projections. The cell cavity is filled with 
a reddish-brown contents which are somewhat fissured. 

Clustered unicellular hairs occur on the leaves of chestnut, 
witch-hazel, althea, European oak, etc. In European oak (Plate 
8, Figs. 1 and 2) clusters of two and three hairs occur. The 
walls are yellowish- white, smooth, and the tip of the hair is solid. 

In kamala (Plate 8, Fig. 3) clusters of seven or more hairs 
occur; the walls are yellowish, and the cell cavity is reddish- 
brown. In witch-hazel leaf (Plate 8, Fig. 4) clusters of a variable 
number of hairs occur. The hairs, which are of various lengths, 
have yellowish-white, thick, smooth walls, and reddish cell 
contents. 

In althea leaf (Plate 8, Fig. 5) the hairs are nearly straight 
and the walls are smooth. The basal portions of the hair are 
strongly pitted. 

Branched solitary unicellular hairs occur on the leaves of 
hesperis matronalis (Plate 7, Fig. 8), and on galphimia glauca 
(Plate 7, Fig. 9). 

The hair of hesperis matronalis has smooth walls, and the 
two branches grow out nearly parallel to the leaf surface. 

The hair of galphimia glauca has rough walls, and the two 
branches grow upward in a bifurcating manner. 

MULTICELLULAR HAIRS 

Multicellular hairs are divided into the uniseriate and the 
multiseriate hairs. Both of these groups are divided into the 
branched and the non-branched hairs, as follows: 

1. Uniseriate. 

(^4) Non-branched. 
(B) Branched. 

2. Multiseriate. 

(^4) Non-branched. 
(B) Branched. 

Multicellular uniseriate non-branched hairs occur on the 
leaves of digitalis, Western and Eastern skullcap, peppermint, 
thyme, yarrow, arnica flowers, and sumac fruit. 

Digitalis hairs (Plate 9, Fig. 1) are made up of a varying 



PLATE 9 




Multicellular Uniseriate Non-Branched Hairs 

1. Digitalis leaf {Digitalis purpurea, L.). 

2. Arnica flower {Arnica montana, L.). 

3. Western skullcap plant {Scutellaria canescens, Nutt.). 

4. Eastern skullcap plant {Scutellaria lateriflora, L.) 

5. Peppermint leaf {Mentha piperita, L.). 

6. Thyme leaf {Thymus vulgaris, L.). 

7. Yarrow flowers {Achillea millefolium, L.). 

8. Wormwood leaf {Artemisia absinthium, L.). 

9. Sumac fruit {Rhus glabra, L.). 



74 



HISTOLOGY OF MEDICINAL PLANTS 



number of uniseriate-arranged cells of unequal length, frequently 
placed at right angles to the cells above and below; the walls 
are of a whitish color, and are rough or smooth. 

Eastern skullcap (Plate 9, Fig. 4) has hairs with not more 
than four cells ; these hairs are curved, and the walls are whitish, 
sometimes smooth, but usually rough. In Western skullcap 
(Plate 9, Fig. 3) the hairs have sometimes as many as seven 
cells. The walls are white and rough, and the individual cells 
of the hair are much larger than are the cells of the hairs of 
true skullcap. 

Peppermint (Plate 9, Fig. 5) has from one to eight cells. 
The hair is curved, and the walls are very rough. 

Thyme (Plate 9, Fig. 6) has short, thick, rough-walled 
trichomes, the terminal cell usually being bent at nearly right 
angles to the other cells. 

Yarrow hairs (Plate 9, Fig. 7) have a variable number of 
cells. In all the hairs the basal cells are short and broad, while 
the terminal cell is greatly elongated. 

Arnica hairs (one form, Plate 9, Fig. 2) have frequently as 
many as four cells, the terminal cell being longer than the basal 
cells. The walls are white and smooth. 

Sumac-fruit hairs (Plate 9, Fig. 9) have spindle-shaped, 
reddish-colored hairs. 

Multicellular multiseriate non-branched hairs occur on 
cumin fruit and on the tubular part of the corolla of calendula. 

The hairs on cumin fruit vary considerably in size. All the 
hairs are spreading at the base and blunt or rounded at the apex. 
The cells forming the hair are narrow and the walls are thick. 
Three differently sized hairs are shown in Plate 10, Fig. 1. 

The hairs of the base of the ligulate petals of calendula 
(Plate 10, Fig. 2) are biseriate. The hairs are very long and 
the walls are very thin. 

Multicellular uniseriate branched hairs occur on the leaves 
of dittany of Crete, mullen, and on the calyx of lavender flowers. 

The dittany of Crete (Plate 11, Fig. 3) hair is smooth- walled, 
and the branches are alternate. 

In mullen (Plate 1 1 , Fig. 1) the hairs have whorled branches, 
the walls are smooth, and the cell cavity usually contains air. 

The lavender hairs (Plate 11, Fig. 2) have mostly opposite 



PLATE 10 




Multicellular Multiseriate Non-Branched Hairs 

1. Cumin (Cuminum cyminum, L.). 

2. Marigold {Calendula officinalis, L.). 



PLATE ii 





THE EPIDERMIS AND PERIDERM 



77 



branches, and the walls are rough. Thus the multicellular 
branched hairs may be divided into subgroups which have 
alternate, opposite, whorled, or in certain hairs irregularly ar- 
ranged branches. Each class may be again subdivided accord- 
ing to color, character of cell termination, etc., as cited at the 
beginning of the chapter. 

Occasionally multicellular hairs assume the form of a shield 
(Plate 12, Fig. i); in such cases the hair is termed peltate, as in 
the non-glandular multicellular hair of shepherdia canadensis. 

Hairs grow out from the surface of the epidermis in a per- 
pendicular, a parallel, or in an oblique direction. Hairs which 
grow parallel or oblique to the surface are usually curved, and 
the outer curved part of the wall is usually thicker than the 
inner curved wall. 

The mature hairs of some plants consist of dead cells. In 
other plants the cells forming the hair are living. When dried, 
those hairs, which were dead before drying, contain air; while 
those hairs which were living before drying, show great variation 
in color and in the nature of the cell contents. The contents 
are either organic or inorganic. The commonest organic con- 
stituent is dried protoplasm. In cannabis indica are de- 
posits of calcium carbonate. 

Multicellular multiseriate branched hairs are the ultimate 
division of the pappus of erigeron, aromatic goldenrod, arnica, 
grindelia, boneset, and life-everlasting. 

The hairs of erigeron (Plate 13, Figs. 1 and 2) are slender; 
the walls are porous. Each hair terminates in two cells, which 
are greatly extended and sharp-pointed; the branches from the 
basal part of the hairs (Plate 13, Fig. 1) are of about the same 
length as the apical branches. 

The hairs of aromatic goldenrod (Plate 13, Figs. 3 and 4) are 
larger than those of erigeron; the diameter is greater and the 
walls are non-porous. The apex of the hair terminates in a 
group of about four cells of unequal length, which are sharp- 
pointed. The branches of the basal cells (Plate 13, Fig. 3) are 
similar to the branches of the apical cells. 

The hairs of arnica (Plate 14, Figs. 1 and 2) have thick, 
strongly porous walls; the branches terminate in sharp points. 
The apex of the hair terminates in a single cell. The basal 



PLATE 12 




Non-Glandular Multicellular Hairs 
Shepherctia canadensis, [L.] Nutt. 




Multicellular Multiseriate Branched Hairs 

1. Basal hairs of erigeron (Erigeron canadensis , L.). 

2. Apical hairs of erigeron (Erigeron canadensis, L.). 

3. Basal hairs of aromatic goldenrod (Solidago odora, Ait.). 

4. Apical hairs of aromatic goldenrod (Solidago odora, Ait.). 



80 



HISTOLOGY OF MEDICINAL PLANTS 



branches (Plate 14, Fig. 2) are much longer than special 
branches. 

The hair of grindelia (Plate 14, Figs. 3 and 4) has very thick 
walls with numerous elongated pores. The apex of the hair 
terminates in a cluster of cells with short, free, sharp-pointed 
ends. The basal branches (Plate 14, Fig. 4) are longer than 
the apical branches. 

Boneset hair (Plate 15, Figs. 1 and 2) has non-porous walls. 
The apex of the hair terminates in two blunt-pointed cells. 
The terminal wall is thicker than the side wall. Some of the 
branches lower down terminate in cells with very thick or solid 
points. The basal branches (Plate 15, Fig. 1) are longer, but 
the cells are narrower and more strongly tapering than are the 
branches of the apical part of the hair. 

Life-everlasting (Plate 15, Figs. 3 and 4) has uniformly 
thickened but non-porous walls. The hair terminates in two 
blunt-pointed, greatly elongated cells. 

The basal branches (Plate 15, Fig. 4) are narrower, slightly 
tapering, and the base of the branches frequently curve down- 
ward. 

The cell cavities of these hairs are filled with air. 
The walls of hairs are usually composed of cutin; in some 
hairs, of lignin; in other hairs, of cellulose. 

PERIDERM 

The periderm is the outer protective covering of the stems 
and roots of mature shrubs and trees. The periderm replaces 
the epidermis. The periderm may be composed of cork cells, 
stone cell-cork, or a mixture of cork, parenchyma, fibres, stone 
cells, etc. 

CORK PERIDERM 

The typical periderm is made up of cork cells. Cork cells 
vary in appearance, according to the part of the cell viewed. 

On surface view (Plate 16, Fig. A) the cork cells are angled 
in outline and are made up of from four to seven side walls; 
five- and six-sided cells are more common than the four- and 
seven-sided cells. Surface sections of cork cells show their 



PLATE 15 




Multicellular Multiseriate Branched Hairs 

1. Apical hairs boneset {Eupatorium perfoliatum, L.). 

2. Basal hairs boneset (Eupatorium perfoliatum, L.). 

3. Apical hairs life-everlasting (Gnaphalium obtusifolium, L.). 

4. Basal hairs life-everlasting (Gnaphalium obtusifolium, L.). 



THE EPIDERMIS AND PERIDERM 



83 



length and width. These side walls usually appear nearly white, 
while the end wall, particularly of the outermost cork cells, 
usually appears brown or reddish-brown, or in some cases nearly 
black. 

Cork cells on cross-section are rectangular in form, and they 
are arranged in superimposed rows, the number of rows being 
gradually increased as the plant grows older. Such an increase 
in the number of rows of cork cells is shown in the cross-section 
of cascara sagrada (Plate 16, Fig. C). 

Cork cells fit together so closely that there is no intercellular 
spaces between the cells. In this case two rows of cork cells 
occupy no greater space than the solitary row of cork cells 
immediately over and external to them. As a rule, the outer- 
most layers of cork cells have a narrower radial diameter than 
the cork cells of the underlying layers. This is due to the fact 
that these outer cells are stretched as the stem increases in 
diameter. This view shows the height of cork cells, but not 
always the length, which will, of course, vary according to the 
part of the cell cut across. In a section a few millimeters in 
diameter, however, all the variations in size may be observed. 
The color of the walls is nearly white. 

The cavity may contain tannin or other substances. When 
tannin is present, the cavity is of a brownish or brownish-red 
color, or it may be nearly black. Most barks appear devoid of 
any colored or colorless cell contents. 

The radial section (Plate 16, Fig. B) of cork cells shows the 
height of the cells and the width of the cells at the point cut 
across. Some cells will be cut across their longest diameter, while 
others will be cut across their shortest diameter. Cork cells are, 
therefore, smaller in radial section than they are in cross-section. 
The color of the walls is white, and the color and nature of the 
cell contents will vary for the same reasons that they vary in 
cross-sections. 

The number of layers of cork cells occurring in cross- and 
radial-sections varies according to the age of the plant, to the type 
of plant, and to the conditions under which the plant is growing. 

The number of layers of cork cells is not of diagnostic im- 
portance, nor is the surface view of cork cells diagnostic except 
in certain isolated cases. 



PLATE 16 



1 QgsgBsg 




Periderm of Cascara Sagrada (Rhamnus purshiana, D.C.) 

^4. i, Outline of cork cells; 2, Line of contact of adjoining cork cells. 

B. Radial longitudinal section of cascara sagrada. 1, Cork cells; 2,Phel- 
logen; 3, Forming parenchyma cells; 4, Cortical parenchyma cells. 

C. Cross-section of cascara sagrada. 1, Cork cells; 2, Phellogen; 3, Form- 
ing parenchyma cells; 4, Cortical parenchyma cells. 



THE EPIDERMIS AND PERIDERM 



85 



The presence or absence of cork or epidermal tissue in pow- 
ders must always be noted. The presence of cork enables one to 
distinguish Spanish from Russian licorice. In like manner, the 
presence of epidermis enables one to distinguish the pharma- 
copoeial from the unofficial peeled calamus. The absence of 
epidermis in Jamaica ginger is one of the means by which this 
variety is distinguished from the other varieties of ginger, etc. 

In canella alba the periderm is replaced by stone cell-cork. 
That is, the cells forming the periderm are of a typical cork 
shape, but the walls are lignified, unequally thickened, and 
the inner or thicker walls are strongly porous, and the walls 
are of a yellowish color. Stone cell-cork forms the periderm 
of clove bark also, but the cells are narrower and longer, and 
the inner wall is not so thick or porous as is the case in canella 
alba bark. 

STONE CELL PERIDERM 

In canella alba (Plate 17, Fig. B) cork periderm is frequently 
replaced by stone cells, particularly in the older barks. These 
stone cells form the periderm because they replace the cork 
periderm, which fissures and scales off as the root increases 
in diameter. 

The side and end walls of cork cells are of nearly uniform 
diameter. Exceptions occur, but they are not common. In 
buchu stem (Plate 101, Fig. 3), the cork ceUs have thick outer 
walls, but thin sides and inner walls. The cell cavity contains 
reddish-brown deposits of tannin. 

PARENCHYMA AND STONE CELL PERIDERM 

As the trees and shrubs increase in diameter, cracks or fis- 
sures occur in the periderm, or corky layer. In such cases the 
phellogen cells divide and redivide in such manner as to cut 
off a portion of the parenchyma cells, stone cells, and fibres of 
the cortex which is inside of and below the fissure. All the 
parenchyma cells, etc., exterior to the newly formed cork cells 
soon lose their living-cell contents, since their food-supply is 
cut off by the impervious walls of the cork cells. In time they 
are forced outward by the developing cork cells until they 



PLATE 17 




A. Cross-section of Mandrake Rhizome (Podophyllum peltatum, L.). 

1. Epidermis. 

2. Phellogen. 

3. Cortical parenchyma. 

B. Stone cell periderm of white cinnamon (Canella alba, Murr.). 



88 



HISTOLOGY OF MEDICINAL PLANTS 



partially or completely fill the break in the periderm. In white 
oak bark (Plate 18), as in other barks, a large part of the peri- 
derm is composed of dead and discolored cortical cells. 

OEIGIN OF CORK CELLS 

The cork cells are formed by the meristimatic phellogen ' 
cells, which originate from cortical parenchyma. These cells 
divide into two cells, the outer changing into a cork cell, while 
the inner cell remains meristimatic. In other instances the 
outer cell remains meristimatic, while the inner cell changes 
into a cortical parenchyma cell. The development of a cortical 
parenchyma cell from a divided phellogen cell is shown in Plate 
101 , Fig. 6. Both the primary and secondary cork cells originate 
from the phellogen or cork cambrium layer. Cork cells do not 
contain living-cell contents; in fact, in the majority of medicinal 
barks the cork cells contain only air. 

The walls of typical cork cells are composed, at least in part, 
of suberin, a substance which is impervious to water and gases. 
In certain cases layers of cellulose, lignin, and suberin have been 
identified. Suberin, however, is present in all cork cells, and 
in some cases all of the walls of cork cells are composed of suberin. 

Suberized cork cells are colored yellow with strong sodium 
hydroxide solutions and by chlorzinciodide. 



CHAPTER III 



MECHANICAL TISSUES 

The mechanical tissues of the plant form the framework 
around which the plant body is built up. These tissues are 
constructed and placed in such a manner in the different organs 
of the plant as to meet the mechanical needs of the organ. Many 
underground stems and roots which are subjected to radial pres- 
sure have the hypodermal and endodermal cells arranged in the 
form of a non-compressible cylinder. Such an arrangement is 
seen in sarsaparilla root (Plate 38, Fig. 4). The mechanical 
tissue of the stem is arranged in the form of solid or hollow 
columns in order to sustain the enormous weight of the branches. 
In roots the mechanical tissue is combined in ropeiike strands, 
thereby effectively resisting pulling stresses. The epidermis of 
leaves subjected to the tearing force of the wind has epidermal 
cells with greatly thickened walls, particularly at the margin of 
the leaf. The epidermal cells of most seeds have very thick 
and lignified cell walls, which effectively resist crushing forces. 

The cells forming mechanical tissues are: bast fibres, wood 
fibres, collenchyma cells, stone cells, testa epidermal cells, and 
hypodermal and endodermal cells of certain plants. The walls 
of the cells forming mechanical tissues are thick and lignified, 
with the exception of the collenchyma cells and a few of the 
fibres. Lignified cells are as resistive to pulling and other 
stresses as similar sized fragments of steel. The hardness of. 
their wall and their resistance to crushing explain the fact that 
they usually retain their form in powdered drugs and foods. 

BAST FIBRES 

One of the most important characters to be kept in mind in 
studying bast fibres is the structure of the wall. In fact, the 
author's classification of bast fibres is based largely on wall 

89 



90 



HISTOLOGY OF MEDICINAL PLANTS 



structure. Such a classification is logical and accurate, because 
it is based upon permanent characters. Another character used 
in classifying bast fibres is the nature of the cell, whether branched 
or non-branched. In fact, this latter character is used to separate 
all bast fibres into two fundamental groups — namely, branched 
bast fibres and non-branched bast fibres. The third important 
character utilized in classifying fibres is the presence or absence 
of crystals. 

Bast fibres are classified as follows: 

1 . Crystal bearing. 

2. Non-crystal bearing. 

The crystal-bearing fibres are divided into two classes: 

1 . Of leaves. 

2, Of barks. 

The non-crystal bearing are divided into : 

1. Branched. 

2. Non-branched. 

The branched and non-branched are divided into four classes : 

1. Non-porous and non-striated. 

2. Porous and non-striated. 

3. Striated and non-porous. 

4. Porous and striated. 

CRYSTAL-BEARING BAST FIBRES 

The crystal-bearing fibres are composed (1) of groups of 
fibres, (2) of crystal cells, and (3) of crystals. In these cases 
the groups of fibres are large, and they are frequently completely 
covered by crystal cells, which may or may not contain a crystal. 
The crystals found on the fibres from the different plants vary 
considerably in size and form. As a rule, the fibres when sepa- 
rated are free of crystal cells and crystals. This is so because 
the crystal cells are exterior to the fibres, and in separating the 
fibres during the milling process the crystal cells are broken down 
and removed from the fibres. It is common, therefore, to find 
isolated fibres and crystals associated with the crystal-bearing 
fibres. The fibres which are crystal-bearing may be striated 
or porous, etc.; but owing to the fact that the grouping of the 
fibres and crystals is so characteristic, little or no attention is 
paid to the structure of the individual fibres. 



PLATE 19 





3 O 




1 r f loi 




\ 




t 1 








Crystal-Bearing Fibres of Barks 

1. Frangula (Rhamnus frangula, L.). 

2. Cascara sagrada (Rhamnus purshiana, D.C.). 

3. Spanish licorice (Glycyrrhiza glabra, L.). 

4. Witch-hazel bark (Hamamelis virginiana, L.). 



92 



HISTOLOGY OF MEDICINAL PLANTS 



Crystal-bearing fibres occur in the barks of frangula (Plate 
19, Fig. 1); cascara sagrada (Plate 19, Fig. 2); witch-hazel 
(Plate 19, Fig. 4); in cocillana (Plate 20, Fig. 1); in white oak 
(Plate 20, Fig. 2); in quebracho (Plate 20, Fig. 3); and in 
Spanish licorice root (Plate 19, Fig. 3). 

The crystal-bearing fibres of leaves are always associated 
with vessels or tracheids and with cells with chlorophyl. The 
presence or absence of crystal-bearing fibres in leaves should 
always be noted. The crystal-bearing fibres of leaves are 
composed of fragments of conducting cells, fibres, crystal cells, 
and crystals. The crystal-bearing fibres of leaves occur in 
larger fragments than the other parts of the leaf, because the 
fibres are more resistant to powdering. Having observed that 
a leaf has crystal-bearing fibres, in order to identify the powder 
it is necessary to locate one of the other diagnostic elements 
of the leaf — as the papillas of coca (Plate 21, Fig. 1), or the hair 
of senna (Plate 21, Fig. 3), or the vessels in eucalyptus (Plate 21, 
Fig. 2). 

Branched bast fibres occur in only a few of the medicinal 
plants, notable examples being tonga root and sassafras root. 
Occasionally one is found in mezereum bark. 

The bast fibre of tonga root (Plate 22, Fig. 2) often has seven 
branches, but four- and five-branched forms are more common. 
The walls are non-porous, non-striated, and nearly white. 

The bast fibre of sassafras (Plate 22, Fig. 1) has thick, non- 
porous, and non-striated walls, and the branching occurs usually 
at one end only of the fibre. Most of the bast fibres of sassafras 
root are non-branched. 

POROUS AND STRIATED BAST FIBRES 

Porous and striated walled bast fibres occur in blackberry 
bark of root, wild-cherry bark, and in cinchona bark. 

The fibres of blackberry root bark (Plate 23, Fig. 1) have 
distinctly porous and striated walls; the cavity, which is usually 
greater than the diameter of the wall, contains starch. These 
fibres usually occur as fragments. 

In wild-cherry bark (Plate 23, Fig. 2) the fibre has short, 
thick, unequally thickened walls, which are porous and striated. 
Most of the fibres are unbroken. 



PLATE 20 




Crystal-Bearing Fibres of Barks 

1. Cocillana (Gnarea rusbyi, [Britton] Rusby). 

2. White oak (Quercus alba, L.). 

3. Quebracho (Aspidosperma quebracho-bianco, Schlechtendal). 



PLATE 21 




Crystal-Bearing Fibres of Leaves 

1. Coca leaf (Erythroxylon coca, Lam.). 

2. Eucalyptus leaf (Eucalyptus globulus, Labill). 

3. Senna leaf (Cassia angustifolia, Vahl.). 



PLATE 22 




Branched Bast Fibres 

1. Sassafras root bark (Sassafras variifolium, [Salisb.] Kuntze). 

2. Tonga root. 



96 



HISTOLOGY OF MEDICINAL PLANTS 



Yellow cinchona bark (Plate 23, Fig. 3) has very thick, 
prominently striated porous- walled fibres, with either blunt or 
pointed ends. The cavity is narrow, and the pores are simple 
or branched. 

POROUS AND NON-STRIATED BAST FIBRES 

Porous and non-striated bast fibres occur in marshmallow 
root and echinacea root. 

The fibres of marshmallow (Plate 24, Fig. 3) usually occur 
in fragments. The walls have simple pores, and the diameter 
of the cell cavity is very wide; the pores on the upper or lower 
wall are circular or oval in outline (end view) . 

The bast fibres of echinacea root (Plate 24, Fig. 4) are seldom 
broken; the walls are yellow, the pores are simple and numerous. 
The edges and surface of the fibres are* frequently covered with 
a black intercellular substance. 

NON-POROUS AND STRIATED BAST FIBRES 

Non-porous and striated bast fibres occur in elm bark, 
stillingia root, and cundurango bark. The bast fibres of elm 
bark (Plate 25, Fig. 1) occur in broken, curved, or twisted frag- 
ments. The central cavity is very small, and the walls are 
longitudinally striated. 

In powdered stillingia root (Plate 25, Fig. 2) the bast fibres 
are broken, and the wall is very thick and longitudinally striated. 
The central cavity is small and usually not visible. Bast fibres 
of cundurango (Plate 25, Fig. 3) are broken in the powder. 
The cavity is very narrow, and the striations are arranged 
spirally, less frequently transversely. 

NON-POROUS AND NON-STRIATED BAST FIBRES 

Non-porous and non-striated walled bast fibres occur in 
mezereum bark, in Ceylon cinnamon, in sassafras root bark, 
and in soap bark. 

The simplest non-porous and non-striated walled bast fibres 
are found in mezereum bark (Plate 26, Fig. 4). The individual 
fibre is very long. If often measures over three millimeters in 
length, so that in the powder the fibre is usually broken. The 
wall is non-lignified, white, non-porous, and of uniform diameter. 



PLATE 23 




Porous and Striated Bast Fibres 

1. Blackberry root {Rubus cuneifolius, Pursh.). 

2. Wild cherry {Prunus serotina, Ehrh.). 

3. Yellow cinchona {Cinchona species). 




Porous and Non-Striated Bast Fibres 

1. Sarsaparilla root (Hypoderm), {Smilax officinalis, Kunth). 

2. Unicorn root (Endoderm). 

3. Marshmallow root (Althcea officinalis, L.). 

4. Echinacea root (Echinacea angustifolia, D. C). 



PLATE 25 




Non-Porous and Striated Bast Fibres 

1. Elm bark (Ulmus fulva, Michaux). 

2. Stillingia root {Stillingia sylvatica, L.). 

3. Cundurango root bark (Marsdenia cundurango, [Triana] Nichols). 



100 



HISTOLOGY OF MEDICINAL PLANTS 



In Ceylon cinnamon (Plate 26, Fig. 2) the bast fibres measure 
up to .900 mm. in length, so that in powdering the bark the 
fibre is rarely broken. These bast fibres, unlike the bast fibres 
of mezereum, have thick, white walls and a narrow cell cavity. 
Both ends of the fibre taper gradually to a long, narrow point. 

In Saigon cinnamon the bast fibres are not as numerous 
as they are in Ceylon cinnamon. The individual fibres are 
thicker than in Ceylon cinnamon, and the walls are yellowish 
and rough and the ends bluntly pointed. These fibres are rarely 
ever free from adhering fragments of parenchyma tissue. 

In sassafras root bark (Plate 26, Fig. 3) the fibre has one 
nearly straight side — the side in contact with the other bast 
fibres — and an outer side with a wavy outline, caused by the 
fibre's pressing against parenchyma cells, the point of highest 
elevation being the point of the fibre's growth into the inter- 
cellular space between two cells. The outer part of the wall 
tapers gradually at either end to a sharp point. The walls 
are white, thick, and non-porous. 

In soap bark (Plate 26, Fig. 1) the bast fibres have thick, 
white, wavy walls and a narrow cavity. One end of the cell is 
frequently somewhat blunt while the opposite end is slightly 
tapering. 

The branched stone cells of wild-cherry bark have three or 
more branches. The pores are small and usually non-branched, 
and the striations are very fine and difficult to see unless the 
iris diaphragm is nearly closed. The central cavity is very 
narrow and frequently contains brown tannin. 

The branched stone cells of hemlock bark are very large; 
the walls are white and distinctly porous bordering on the cell 
cavity, which contains bright reddish-brown masses of tannin. 

In cross-section bast fibres occur singly or isolated, as in 
Saigon cinnamon (Plate 34, Fig. 1); or in groups, as in meni- 
spermum (Plate 27, Figs. 1 and 2); or in the form of continuous 
bands, as in buchu stem (Plate 100, Fig. 5). 

Bast fibres are seen in longitudinal view in powdered drugs. 
The cell cavity shows throughout the length of the fibre. This 
cavity differs greatly in different fibres. In soap bark (Plate 
26, Fig. 1) there is scarcely any cell cavity, while in mezereum 
bark (Plate 26, Fig. 4) the cell cavity is very large. 



PLATE 26 




Non-Porous and Non-Striated Bast Fibres 

1. Soap bark (Quillaja sapo?iaria, Molina). 

2. Ceylon cinnamon bark (Cinnamomum zeylanicum, Nees). 

3. Sassafras root bark (Sassafras variifolium, [Salicb.] Kuntze). 

4. Mezereum bark (Daphne mezereum, L.). 



PLATE 27 




Groups of Bast Fibres 

1. Menispermum rhizome {Menispermum canadensis, L.). 

2. Althea root (Althaa officinalis, L.) showing two groups 



MECHANICAL TISSUES 



103 



The pores, which are absent in many drugs, are, when 
present, either simple, as in echinacea root (Plate 24, Fig. 4), 
or they are branched, as in yellow cinchona (Plate 23, Fig. 3). 

In each of the above fibres the length and width of the 
fibre are shown. The fibres also have pores of variable length. 
Such a variation is common to most fibres with pores. That 
part of the wall immediately over or below the cell cavity shows 
the end view or diameter of the pore, as in the fibre of marsh- 
mallow root (Plate 24, Fig. 3). As a rule, however, the pores 
show indistinctly on the upper and lower wall. 

OCCURRENCE IN POWDERED DRUGS 

In powdered drugs bast fibres occur singly or in groups. 
The individual fibres may be broken, as in mezereum and elm 
bark, or they may be entire, as in Ceylon cinnamon and in 
sassafras bark (Plate 26, Figs. 2 and 3). 

The lignified walls of bast fibres are colored red by a solution 
of phlorogucin and hydrochloric acid, and the walls are stained 
yellow by aniline chloride. 

In fact, few of the fibres found in individual plants occur 
in a broken condition. 

Isolated bast fibres are circular in outline. Bast fibres, when 
forming part of a bundle, have angled outlines when they are 
completely surrounded by other bast fibres; but when they 
occur on the outer part of the bundle, and when in contact with 
parenchyma or other cortical cells, they are partly angled and 
partly undulated in outline. 

In the bast fibres the pores are placed at right angles to 
the length of the fibre. The side walls show the length of the 
pore (Plate 24, Fig. 3) ; while the upper or lower wall shows the 
outline, which is circular, and the pore, which is very minute. 

Most bast fibres have no cell contents. In some cases, 
however, starch occurs, as in the bast fibres of rubus. 

The color of the bast fibres varies, being colorless, as in 
Ceylon cinnamon; or yellowish- white, as in echinacea; or bright 
yellow, as in bayberry bark. 

Bast fibres retain their living-cell contents until fully de- 
veloped; then they die and function largely in a mechanical 
way. 



104 



HISTOLOGY OF MEDICINAL PLANTS 



The walls of bast fibres are composed of cellulose or of lignin. 
Most of the bast fibres occurring in the medicinal plants give 
a strong lignin reaction. 

WOOD FIBRES 

Wood fibres always occur in cross-sections associated with 
vessels and wood parenchyma, from which they are distin- 
guished by their thicker walls, smaller diameter, and by the 
nature of the pores, which are usually oblique and fewer in 
number than the pores in the walls of wood parenchyma, and 
different in form from the pores of vessels. 

The wood fibre on cross-section (Plate 105, Fig. 4) shows 
an angled outline, except in the case of the fibres bordering the 
pith-parenchyma, etc., in which case they are rounded on their 
outer surface, but angled at the points in contact with other 
fibres. The pore of wood fibres is one of the main characteristics 
which enable one to distinguish the wood fibres from bast fibres. 

The pores are slanting or strongly oblique (Plate 28, Fig. 2), 
and they show for their entire length on the broadest part of 
the wall — i.e., the upper or the lower surface — while in the side 
wall they are oblique; but they are not so distinct as they are 
on the broad part of the wall. 

Frequently the pores appear crossed when the upper and 
the lower wall are in focus, because the pores are spirally ar- 
ranged, and the pore on the under wall throws a shadow across 
the pore on the upper wall, or vice versa. 

Wood fibres always occur in a broken condition (Plate 28, 
Fig. 1) in powdered drugs. These broken fibres usually occur 
both singly and in groups in a given powder. 

The color of wood fibres varies greatly in the different me- 
dicinal woods. Fragments of wood are usually adhering to 
witch-hazel, black haw, and other medicinal barks. In each of 
these cases the wood fibres are nearly colorless. In barberry 
bark adhering fragments of wood and the individual fibres are 
greenish-yellow. The wood fibres of santalum album are whitish- 
brown; of quassia, whitish-yellow; of logwood and santalum 
rubum, red. 

Some wood fibres function as storage cells. In quassia the 



PLATE 28 




1. White sandalwood (Santalum album, L.). 

2. Quassia wood (Picrtzna excelsa, [Swartz] Lindl.). 

3. Logwood with crystals (Hamatoxylon campechianum, L.). 

4. Black haw root (Viburnum prunifolium, L.). 



106 



HISTOLOGY OF MEDICINAL PLANTS 



wood fibres frequently contain storage starch. The wood fibres 
of logwood and red saunders contain coloring substances, which 
are partially in the cell cavity and partially in the cell wall. 
The walls of wood are composed largely of lignin. 

COLLENCHYMA CELLS 

Collenchyma cells form the principal medicinal tissue of 
stems of herbs, petioles of leaves, etc. In certain herbs the 
collenchyma forms several of the outer layers of the cortex of 
the stem. In motherwort, horehound, and in catnip the col- 
lenchyma cells occur chiefly at the angles of the stem. In 
motherwort (Plate 29, Fig. B) there are twelve bundles, one 
large bundle at each of the four angles, and two small bundles, 
one on either side of the large bundle. In catnip (Plate 29, 
Fig. A) there are four large masses, one at each angle of 
the stem. 

Collenchyma cells differ from parenchyma cells in a number 
of ways: first, the cell cavity is smaller; secondly, the walls 
are thicker, the greater amount of thickening being at the angles 
of the cells — that is, the part of the cell wall which is opposite 
the usual intercellular space of parenchyma cells, while the wall 
common to two adjoining cells usually remains un thickened. 
In horehound stem (Plate 30, Fig. 2) the thickening is so great 
at the angles that no intercellular space remains. In the side 
column of motherwort stem (Plate 30, Fig. 1) the thickening 
between the cells has taken place to such an extent that the 
cell cavities become greatly separated and arranged in parallel 
concentric rows. 

The collenchyma of the outer angle of motherwort stem 
(Plate 30, Fig. 3) is greatly thickened at the angles. There 
are no intercellular spaces between the cells, and cell cavity 
is usually angled in outline instead of circular, as in the cells 
of horehound. In certain plants intercellular spaces occur be- 
tween the cells, and the walls are striated instead of being non- 
striated, as in the stems of horehound, motherwort, and 
catnip. 

Collenchyma cells retain their living contents at maturity. 
Many collenchyma cells, particularly of the outer layers of 



PLATE 29 




PLATE 30 



)OOOCPOOoq 




0, 



Woo 



>0 



poy n oQp 

pO u n09$ 
'ooOrpcf 



^ u x dO^M 



COLLENCHYMA CELLS 

1. Cross-section of a side column of the collenchyma of motherwort stem 
(Leonurus cardiaca, L.). 

2. Cross-section of the collenchyma of horehound stem (Marrubium 
vulgare, L.). 

3. Cross- section of the collenchyma of the outer angle of motherwort stem. 



MECHANICAL TISSUES 



109 



bark and the collenchyma of the stems of herbs, contain 
chlorophyll. 

The walls of collenchyma consist of cellulose. 

STONE CELLS 

Stone cells, like bast fibres, are branched or non-branched. 
Each group is then separated into subgroups according to wall 
structure (whether striated, or pitted and striated, etc.), thick- 
ness of wall and of cell cavity, color of wall and of cell contents, 
absence of color and of cell contents, etc. 

BRANCHED STONE CELLS 

Branched stone cells occur in a number of drugs. In witch- 
hazel bark (Plate 31, Fig. 2) the walls are thick, white, and very 
porous. In some cells the branches are of equal length; in 
others they are unequal. In the tea-leaf (Plate 31, Fig. 1) the 
walls are yellowish white and finely porous. When the lower 
wall is brought in focus, it shows numerous circular pits. These 
pits represent the pores viewed from the end. The branches 
frequently branch or fork. 

Branched stone cells also occur in coto bark, acer spicatum, 
staranise, witch-hazel leaf, hemlock, and wild-cherry barks. 

Non-branched stone cells are divided into two main groups, 
as follows: 

1. Porous and striated stone cells, and, 

2. Porous and non-striated stone cells. 

POROUS AND STRIATED STONE CELLS 

Porous and striated walled stone cells occur in ruellia root, 
winter's bark, bitter root, allspice, and aconite. These stone 
cells are shown in Plate 33, Figs. 1, 2, 3, 4, and 5. 

The stone cells of ruellia root (Plate 32, Fig. 1) are greatly 
elongated, rectangular in form, with thick, white, strongly 
porous walls. The central cavity is narrow and is marked with 
prominent pores and striations. 

The stone cells of winter's bark (Plate 32, Fig. 2) vary from 
elongated to nearly isodiametric. The pores are very large, 




Branched Stone Cells 



1. Tea leaf {Thea sinensis, L.). 

2. Witch-hazel bark (Hamamelis virginiana, L.)- 

3. Hemlock bark (Tsuga canadensis, [L.] Carr). 

4. Wild-cherry bark (Prunus serotina, Ehrh.). 



MECHANICAL TISSUES 



111 



the light yellowish wall is irregularly thickened, and the central 
cavity is very large. The pores are prominent. 

The stone cell of bitter root (Plate 32, Fig. 3) is nearly 
isodiametric. The walls are yellowish white and strongly por- 
ous and striated. The central cavity is about equal to the thick- 
ness of the walls. 

The stone cell of allspice (Plate 32, Fig. 4) is mostly rounded 
in form, and when the outer wall only is in focus it shows numer- 
ous round and elongated pores. The central cavity is filled 
with masses of reddish-brown tannin. The striations are very 
prominent. 

The diagnostic stone cell of aconite (Plate 32, Fig. 5) is 
rectangular or square in outline; the walls are yellowish and 
the central cavity has a diameter many times the thickness of 
the wall. The side and surface view of the pores is prominent, 
and the striations are very fine. 

POROUS AND NON-STRIATED STONE CELLS 

Porous and non-striated stone cells occur in Ceylon cinna- 
mon, in calumba root, in dogwood bark, in cubeb, and in echi- 
nacea root. 

The diagnostic stone cells of Ceylon cinnamon (Plate 33, 
Fig. 1) are nearly square in outline; the walls are strongly 
porous and the large central cavity frequently contains 
starch. 

The stone cells of calumba root (Plate 33, Fig. 2) vary in 
shape from rectangular to nearly square, and the walls are 
greenish yellow, unequally thickened, and strongly porous. 
The typical stone cells contain several prisms, usually four. 

The stone cells of dogwood bark (Plate 33, Fig. 3) have 
thick, white walls with simple and branched pores. The cen- 
tral cavity frequently branches and appears black when recently 
mounted, owing to the presence of air. 

The stone cells of cubeb (Plate 33, Fig. 4) are very small, 
mostly rounded in outline, with a great number of very fine 
simple pores which extend from the outer wall to the central 
cavity. The wall is yellow and very thick. 

The stone cells of echinacea root (Plate 33, Fig. 5) are very 
irregular in form; the walls are yellowish and porous, and the 



112 



HISTOLOGY OF MEDICINAL PLANTS 



central cavity is very large. A black intercellular substance 
is usually adhering to portions of the outer wall. 

The color of the walls of the different stone cells is very 
variable. In Ceylon cinnamon and ruellia the walls are color- 
less; in zanthoxyhum, light yellow; in rumex, deep yellow; 
in cascara sagrada, greenish yellow. 

The pores of stone cells, like the pores of bast fibres, are 
either simple or branched, and they may or may not extend 
through the entire wall. Many of the shorter pores extend for 
only a short distance from the cell cavity. 

The width of the cell cavity varies considerably in the stone 
cells of the different plants. In aconite (Plate 32. Fig. 5), in 
calumba (Plate 33. Fig. 2), and in Ceylon cinnamon (Plate 33, 
Fig. 1), the cell cavity is several times greater than the thick- 
ness of the cell wall. 

In allspice (Plate 32. Fig. 4). in bitter root (Plate 32. Fig. 
3), the diameter of the cell cavity and the thickness of the wall 
are about equal. In cubeb (Plate 33, Fig. 4), in ruellia (Plate 
32, Fig. 1), the wall is thicker than the diameter of the cell 
cavity. 

The cavity of many stone cells contains no characteristic 
cell contents. In other stone cells the cell contents are as 
characteristic as the stone cell. The stone cells of both Saigon 
and Ceylon cinnamon (Plate 33, Fig. 1) contain starch; the 
stone cells of calumba (Plate 33, Fig. 2) contain prisms of calcium 
oxalate; the stone cells of allspice and sweet-birch bark contain 
tannin. 

In cross-sections, stone cells occur singly, as in Saigon cinna- 
mon (Plate 34, Fig. i) 3 ruellia (Plate 34. Fig. 2); in groups, as 
in cascara sagrada (Plate 34, Fig. 3); and in continuous bands, 
as in Saigon cinnamon (Plate 34, Fig. 4). 

In powdered drugs, stone cells, like bast fibres, occur as in 
ruellia, calumba, etc.; or in groups, as in cascara sagrada. witch- 
hazel bark, etc. In most oowders they occur both singly and 
in groups. 

The individual stone cells are mostly entire, as in ruellia, 
calumba, allspice, echinacea, etc. In cascara sagrada many of 
the stone cells are broken when the closely cemented groups 
are torn apart in the muling process. Many of the branched 



PLATE 32 




Porous and Striated Stone Cells 

1. Ruellia root {Ruellia ciliosa, Pursh.). 

2. Winter's-bark (Drimys winteri, For St.). 

3. Bitterroot (Apocynum androscemifolium, L.). 

4. Allspice (Pimenta officinalis, LindL). 

5. Aconite (Aconitum napellus, L.). 



PLATE 33 




Porous and Non-Striated Stone Cells 
. Ceylon cinnamon (cinnamomum zeylanicum, Nees). 
. Calumba root (Jateorhiza palmata, [Lam.] Miers). 
. Dogwood root bark (Cornus fiorida, L.). 
. Cubeb {Piper cubeba, L., f.) 
. Echinacea (Echinacea angustifolia, D.C.). 



PLATE 34 




116 



HISTOLOGY OF MEDICINAL PLANTS 



stone cells of witch-hazel bark and leaf, wild cherry, etc., also 
occur broken in the powder. 

The walls of all stone cells are composed of lignin. 

The form of stone cells varies greatly; in aconite the stone 
cells are quadrangular; in ruellia they are rectangular; in 
pimenta, circular or oval in outline; in most stone cells they 
are polygonal. 

The lignified walls of stone cells are stained red with a 
solution of phloroglucin and hydrochloric acid, and the walls 
are stained yellow by aniline chloride. 

ENDODERMAL CELLS 

The endodermal cells of the different plants vary greatly 
in form, color, structure, and composition of the wall, yet these 
different endodermal cells may be divided into two groups: 
first, thin-walled parenchyma-like cells, and, secondly, thick- 
walled fibre-like cells. In the thin- walled endodermal cells the 
walls are composed of cellulose, and the cell terminations are 
blunt or rounded. When the drug is powdered the cells break 
up into small diagnostic fragments. In the thick- walled endo- 
dermal cells the walls are lignified and porous, and the ends of 
the cell are frequently pointed and resemble fibres. 

Sarsaparilla root, triticum, convallaria, and aletris have 
thick-walled endodermal cells. 

STRUCTURE OE ENDODERMAL CELLS 

The endodermal cells of sarsaparilla root (Plate 35, Fig. 1) 
are never more than one layer in thickness, The walls are 
porous and of a yellowish-brown color. Alternating with the 
thick-walled cell is a thin-walled cell, which is frequently re- 
ferred to as a passage cell. 

The endodermal cells of triticum (Plate 35, Fig. 2) are yellow- 
ish and the walls are porous and striated. There are one or two 
layers of cells. The cells forming the outer layer have very 
thin outer but thick inner walls, while the cells forming the 
inner layer are more uniform in thickness. 

The endodermal cells of convallaria (Plate 35, Fig. 3) are 
yellowish white in color, and the walls are porous and striated. 



PLATE 35 




4 



Cross-Sections of Endodermal Cells of 

1. Sarsaparilla root (Smilax officinalis, Kunth) . 

2. Triticum (Agropyron repens, L.). 

3. Convallaria (Convallaria majalis, L.) 

4. Aletris (Aletris farinosa, L.). 



118 



HISTOLOGY OF MEDICINAL PLANTS 



The outer wall of the layer of cells is thinner than the inner 
wall. The innermost layer of cell is more uniformly thickened. 

The endodermal cells of aletris (Plate 35, Fig. 4) are yellow- 
ish brown, slightly porous and striated. There are one or two 
layers of these cells, and two of the smaller cells usually occupy 
a space similar to that occupied by the radically elongated 
single cell. 

On longitudinal view the endodermal cells of sarsaparilla 
triticum, convallaria, and aletris appear as follows: 

Those of sarsaparilla (Plate 36, Fig. 1) are greatly elongated, 
the ends of the cells are blunt or slightly pointed, and the walls 
appear porous and striated. 

Those of triticum (Plate 36, Fig. 2) are elongated, the walls 
are porous and striated, and the outer wall is much thinner 
than the inner wall. The end wall between two cells frequently 
appears common to the two cells. 

Those of convallaria (Plate 36, Fig. 3) are elongated, and 
the end wall is usually blunt. The outer wall is thinner than 
the inner wall. 

Those of aletris (Plate 36, Fig. 4) are fibre-like in appear- 
ance; the ends of the cells are pointed and the wall is strongly 
porous. The longitudinal view of these cells is shown in plate 36. 

HYPODERMAL CELLS 

Hypodermal cells occur in sarsaparilla root and in triticum. 
In the cross-section of sarsaparilla root (Plate 37, Fig. 1) the 
hypodermal cells are yellowish or yellowish brown. The outer 
wall is thicker than the inner wall, the cell cavity is mostly 
rounded, and contains air. The walls are porous and finely 
striated. On longitudinal view the hypodermal cells of sarsa- 
parilla (Plate 37, Fig. 2) are greatly elongated; the outer and 
side walls are thicker than the inner walls. The ends of the 
cells are blunt and distinct from each other. 

In cross-section the hypodermal cells of triticum (Plate 37, 
Fig. 3) are nearly rounded in outline, and the walls are of nearly 
uniform thickness. In longitudinal view (Plate 37, Fig. 4) 
the same cells appear parenchyma-like, and the walls between 
any two cells appear common to the two cells. 



PLATE 36 




Longitudinal Sections of Endodermal Cells 

1. Sarsaparilla root (Smilax officinalis, Kunth). 

2. Triticum (Agropyron repens, L.). 

3. Convallaria (Convallaria i?iajalis, L.). 

4. Aletris (Aletris farinosa, L.). 



PLATE 37 




Hypodermal Cells 



1. Cross-section sarsaparilla root (Smile x officinalis, Kunth). 

2. Longitudinal section sarsaparilla root (Smilax officinalis, Kunth). 

3. Cross-section triticum (Agropyron repens, L.). 

4. Longitudinal section triticum (Agropyron repens, L.). 



CHAPTER IV 



ABSORPTION TISSUE 

Most plants obtain the greater part of their food, first, from 
the soil in the form of a watery solution, and, secondly, from the 
air in the form of a diffusible gas. In a few cases all the food 
material is obtained from the air, as in the case of epiphytic 
plants. In such plants the aerial roots have a modified outer 
layer — velarnen — which functions as a water-absorbing and gas- 
condensing tissue. Many xerophytic plants absorb water 
through the trichomes of the leaf. Such absorption tissue 
enables the plant to absorb any moisture that may condense 
upon the leaf and that would not otherwise be available to the 
plant. The water-absorbing tissue of roots is restricted to the 
root hairs, which are found, with few exceptions, only on young 
developing roots. 

ROOT HAIRS 

Root hairs usually occur a short distance back of the root 
cap. There is, in fact, a definite zone of the epidermis on which 
the root hairs develop. This zone is progressive. As the root 
elongates the root hairs continue to develop, the zone of hairs 
always remaining at about the same distance from the root 
cap. With the development of new zones of growth the hairs 
on the older zone die off and finally become replaced by an epi- 
dermis, or a periderm, except in the case of sarsaparilla root, and 
possibly other roots that have persistent root hairs. 

Each root hair is an outgrowth from an epidermal cell (Plate 
38, Fig. 3). The length of the hair and its form depend upon 
the nature of the soil, whether loose or compact, and upon the 
amount of water present. 

A root hair is formed by the extension of the peripheral wall 
of an epidermal cell. At first this wall is only slightly papillate, 
but gradually the end wall is extended farther and farther from 

121 



122 



HISTOLOGY OF MEDICINAL PLANTS 



the surface of the root, caused by the development of side 
walls by the growing tip of the root hair until a tube-like struc- 
ture, root hair, is produced. The root hair is then a modified 
epidermal cell. The protoplast lines the cell, and the central 
part of the root hair consists of a large vacuole rilled with cell 
sap. The wall of the root hair is composed of cellulose, and 
the outermost part is frequently mucilaginous. As the root 
hairs develop, they become bent, twisted, and of unequal diam- 
eter, as a result of growing through narrow, winding soil 
passages. During their growth, the root hairs become firmly 
attached to the soil particles. The walls of root hairs give an 
acid reaction caused by the solution of the carbon dioxide ex- 
creted by the root hair. The acid character of the wall attracts 
moisture, and in addition has a solvent action on the insoluble 
compounds contained in the soil. It will thus be seen that the 
method of growth, structure, composition, and reaction of the 
wall of the root hair is perfectly suited to carry on the work 
of absorbing the enormous quantities of water needed by the 
growing plant. It is a well-known fact that when two solutions 
of unequal density are separated by a permeable membrane, 
the less dense liquid will pass through the membrane to the 
denser liquid. The wall of the root hair acts like an osmatic 
membrane. The less dense watery solution outside the root 
hair passes through its wall and into the denser cell sap solution. 
As the solution is absorbed, it passes from the root hair into 
the adjoining cortical parenchyma cells. 

It is a fact that root hairs are seldom found in abundance 
on medicinal roots. This is due to the fact that root hairs 
occur only on the smaller branches of the root, and that when 
the root is pulled from the ground the smaller roots with their 
root hairs are broken off and left in the soil. For this reason 
a knowledge of the structure of root hairs is of minor importance 
in the study of powdered drugs. An occasional root hair is 
found, however, in most powdered roots, but root hairs have 
little or no diagnostic value, except in false unicorn root and 
sarsaparilla. When false unicorn root is collected, most of the 
root hairs remain attached to the numerous small fibrous roots, 
owing to the fact that these roots are easily removed from the 
sandy soil in which the plants grow. The root hairs of false 



PLATE 38 




Cross-Section of Sarsaparilla Root (Smilax officinalis, Kunth) 

1 . Epidermal cell developing into a root hair. 

2. Developing root hair. 

3. Nearly mature root hair. 

4. Hypodermal cells. 



PLATE 39 




ABSORPTION TISSUE 



125 



unicorn are so abundant and so large that they form dense 
mats, which are readily seen without magnification. These 
hairs are, therefore, macroscopically as well as microscopically 
diagnostic. The root hairs of false unicorn (Plate 39, Fig. 2) 
have white, wavy, often decidedly indented walls. The terminal, 
or end wall, is rounded and much thicker than the side walls. 

In sarsaparilla (Plate 39, Fig. 1) the root hairs are curved 
and twisted. The end wall is thicker than the side walls. In 
some hairs the walls are as thick as the walls of the thin-walled 
bast fibres. This accounts for the fact that the root hairs 
are persistent on even the older portions of sarsaparilla root, 
and it serves also to explain why these root hairs remain on 
the root even after being pulled from the firmly packed earth 
in which the root grows. 

WATER ABSORPTION BY LEAVES 

In many xerophytic terrestrial plants, the trichomes occurring 
on leaves act as a water-absorbing tissue. In such plants the 
walls of the hairs are composed largely of cellulose. It is ob- 
vious that these hairs absorb the water of condensation caused 
by dew and light rains — water which could not reach the plant 
except by such means. 

There is no special tissue set aside for the absorption of 
gases from the air. Carbon dioxide, which contributes the 
element carbon to the starch formed by photosynthesis, enters 
the leaf by way of the stoma and lenticels. The structure and 
the chief functions of these will be considered under aerating 
tissue. 



CHAPTER V 



CONDUCTING TISSUE 

All cells of which the primary or secondary function is that 
of conduction are included under conducting tissue. It will 
be understood how important the conducting tissue is when the 
enormous quantity of water absorbed by a plant during a 
growing season is considered. It will then be realized that 
the conducting system must be highly developed in order to 
transport this water from one organ to another, and, in fact, 
to all the cells of the plant. Special attention must be given to 
the occurrence, the structure, the direction of conduction, and 
to the nature of the conducted material. 

The cells or cell groups comprising the conducting tissue 
are vessels and tracheids, sieve tubes, medullary ray cells, latex 
tubes, and parenchyma. 

VESSELS 

Vessels and tracheids form the principal upward con- 
ducting tissue of plants. They receive the soil water expressed 
from the cortical parenchyma cells located in the region of the 
root, immediately back of the root hair zone. This soil water, 
with dissolved crude inorganic and organic food materials, after 
entering the vessels and tracheids passes up the stem. The 
cells needing water at the different heights absorb it from the 
vessels, the excess finally reaching the leaves. When the stem 
branches, the water passes into the vessels of the branches and 
finally to the leaves of the branch. In certain special cases the 
vessels conduct upward soluble food material. In spring sugary 
sap flows upward through the vessels of the sugar maple. 

Vessels are tubes, often of great length, formed from a number 
of superimposed cells, in which the end walls have become 
absorbed. The vessels therefore offer little resistance to the 
transference of water from the roots to the leaves of a plant. 

126 



CONDUCTING TISSUE 



127 



The combined length of the vessels is about equal to the height 
of the plant in which they occur. The length of the individual 
vessels varies from a fraction of a meter up to several meters. 

ANNULAR VESSELS 

The annular vessels are thickened at intervals in the form 
of rings (Plate 40, Fig. 1), which extend outward from and 
around the inner wall of the vessel. In fact, it is the inner wall 
which is thickened in all the different types of vessels. The 
ring-like thickening usually separates from the wall when the 
drug is powdered. Such separated rings occur frequently in 
powdered digitalis, belladonna, and stramonium leaves. An- 
nular vessels are not, however, of diagnostic importance, be- 
cause more characteristic cells are found in the plants in which 
they occur. Not infrequently a vessel will have annular thick- 
enings at one end and spiral thickenings at the other. Such 
vessels are found in the pumpkin stem (Plate 40, Fig. 1). 

Vessels are distinguished from other cells by their arrange- 
ment, by their large size when seen in cross-section, and by the 
thickening of the wall when seen in longitudinal sections of the 
plant or in powders. The side walls of vessels are thickened in 
a number of striking yet uniform ways. The chief types of 
thickening of the wall, beginning with one that is the least 
thickened, are annular, spiral, sclariform, pitted, and pitted 
with bordered pores. 

SPIRAL VESSELS 

In the spiral vessel the thickening occurs in the form of a 
spiral, which is readily separated from the side walls. This is 
particularly the case in powdered drugs, where the spiral thick- 
ening so frequently separates from the cell wall. There are 
three types of spiral vessels: those with one (Plate 41, Fig. 1), 
those with two, and those with three spirals. Single spirals 
occur in most leaves; double spirals occur in many plants 
(Plate 41, Fig. 2), but they are particularly striking in pow- 
dered squills. Triple spirals are characteristic of the eucalyptus 
leaf (Plate 41, Fig. 3); in fact, they form a diagnostic feature 
of the powder. Frequently a spirally thickened wall indicates 
a developmental stage of the vessel. Many such vessels are 



128 



HISTOLOGY OF MEDICINAL PLANTS 



spirally thickened at first, but later, when mature, an increased 
amount of thickening occurs and the vessel becomes a reticulate 
or pitted vessel. Many mature vessels, however, are spirally 
thickened as indicated above. In herbaceous stems and in 
certain roots and leaves spiral vessels are associated with the 
sclariform reticulate and pitted type. In certain cases a single 
spiral band will branch as the vessel matures. 

There is a great variation in the amount of spiral thickening 
occurring in a vessel. In leaves, particularly, the spiral appears 
loosely coiled; while in squills and other rhizomes and roots 
the spiral appears as a series of rings. When viewed by high 
power only half of each spiral band is visible. At either side 
of the cell the exact size and form of the thickening appear in 
two parallel rows of dark circles or projections from the walls. 
This thickening of the wall is rendered visible from the fact 
that the light is retarded as it passes through that portion of the 
spiral extending from the upper to the under side of the spiral; 
while the light readily traverses the upper and lower cross bands 
of the vessel. 

It should be remembered that, when the upper part of the 
spiral vessel is in focus, the bands appear to bend in a direction 
away from the eye; while when the under side of the bands are 
in focus, the bands appear to bend toward the eye. These 
facts will show that it is necessary to focus on both the upper 
and lower walls in studying spiral vessels. In double spiral 
vessels the spirals are frequently coiled in opposite directions; 
therefore the bands appear to cross one another. In eucalyptus 
leaf the three bands are coiled in the same direction. In all 
cases the thickening occurs on all sides of the wall. Its appear- 
ance will, therefore, be the same no matter at what angle the 
vessel is viewed. 

SCLARIFORM VESSELS 

Sclariform vessels have interrupted bands of thickening on 
the inner walls. Two or more such bands occur between the 
two side walls. The series of bands are separated by uniformly 
thickened portions of the wall extending parallel to the length 
of the vessel. Sclariform vessels are usually quite broad, so 
that it is necessary to change the focus several times in order 



PLATE 40 




3. (.4) Upper part of spiral vessel in focus. 
(B) Under part of spiral vessel in focus. 

4. Spiral vessel of the disk petal matricaria (Matricaria 
chamomilla, L.). 



PLATE 41 




Spiral Vessels 



Single spiral vessel of pumpkin stem (Cucurbita pepo, L.). 
Double spiral vessel of squill bulb (Urginea maritima, [L.] Baker). 
Triple spiral /vessel of eucalyptus leaf {Eucalyptus globulus, Labill). 



CONDUCTING TISSUE 



131 



to bring the different series of bands in focus. The series of 
bands are usually of unequal width and length. 

Sclariform vessels occur in male fern (Plate 42, Fig. 2), 
calamus, tonga root (Plate 42, Fig. 3), and sarsaparilla (Plate 

42, Fig. 1). In each they are characteristic. Sclariform vessels, 
with these few exceptions, do not occur in drug plants. In fact, 
drugs derived from dicotyledones rarely have sclariform vessels. 
They occur chiefly in the ferns and drugs derived from mono- 
cotyledenous plants. Their presence or absence should, there- 
fore, be noted when studying powdered drugs. 

RETICULATE VESSELS 

Reticulate vessels are of common occurrence in medicinal 
plants. In fact, they occur more frequently than any other 
type of vessel. The basic structure of reticulate vessels (Plate 

43, Fig. 1) occurring in different plants is similar, but they vary 
in a recognizable way in different plants (Plate 43, Fig. 2). 
The walls of reticulate vessels are thickened to a greater extent 
than are the walls of spirally thickened vessels. 

PITTED VESSELS 

Pitted vessels are met with most frequently in woods and 
wood-stemmed herbs. There are two distinct types of pitted 
vessels — i.e., simple pitted vessels and pitted vessels with 
bordered pores. 

The pitted vessel represents the highest type of cell-wall 
thickening. The entire wall of the vessel is thickened, with 
the exception of the places where the pits occur. The number 
and size of the pits vary greatly in different drugs. In quassia 
(Plate 44, Fig. 1) the pits are numerous and very small, and the 
openings are nearly circular in outline. In white sandalwood 
(Plate 44, Fig. 3) the pits are few in number, but when they 
do occur they are much larger than are the pits of quassia. 

PITTED VESSELS WITH BORDERED PORES 

Pitted vessels with bordered pores are of common occur- 
rence in the woody stems and stems of many herbaceous plants 
(Plate 45, Figs. 3 and 4). In such vessels the wall is un thickened 
for a short distance around the pits. This un thickened portion 



PLATE 42 




SCLARIFORM VESSELS 

1. Sarsaparilla root (Smilax officinalis, Kunth). 

2. Male fern (Dryopteris margi?ialis, [L.] A. Gray). 

3. Tonga root. 



PLATE 43 




Reticulate Vessels 

1. Hydrastis rhizome {Hydrastis canadensis, L.). 

2. Musk root (Ferula sumbul, [Kauffm.] Hook., f.). 



PLATE 44 




Pitted Vessels 



1. Quassia, low magnification {Pier ana excelsa, [Swartz] Lindl.)~ 

2. Quassia, high magnification. 

3. White sandalwood {Santalum album, L.). 



PLATE 45 




Vessels 

1. Reticulate vessel of calumba root (Jateorhiza palmata, [Lam.] Miers). 

2. Reticulate tracheid of hydrastis rhizome (Hydrastis canadensis, L.). 

3. Pitted vessel with bordered pores of belladonna stem. 

4. Pitted vessel with bordered pores of aconite stem (Aconitum napellus,L.). 



136 



HISTOLOGY OF MEDICINAL PLANTS 



may be either circular or angled in outline, a given form being 
constant to the plant in which it occurs. The pits vary from 
oval to circular. Pitted vessels with bordered pores occur in 
belladonna and aconite stems. 

Vessels and tracheids lose their living-cell contents when 
fully developed. In the vessels the cell contents disappear at 
the period of dissolution of the cell walk 

The walls of vessels and tracheids are composed of lignin, 
a substance which prevents the collapsing of the walls when 
the surrounding cells press upon them, and which also prevents 
the tearing apart of the wall when the vessel is filled with ascend- 
ing liquids under great pressure. Lignin thus enables the 
vessel to resist successively compression and tearing forces. 

Tracheids are formed from superimposed cells with oblique 
perforated end walls. The side walls of tracheids are thickened 
in a manner similar to those of vessels. The tracheids in golden 
seal are of a bright-yellow color, and groups of these short 
tracheids scattered throughout the field form the most char- 
acteristic part of the powdered drug. In ipecac root the tracheids 
are of a porcelain- white, translucent appearance, and they are 
much longer than are the tracheids of golden seal. 

The cellulose walls of parenchyma cells are stained blue 
with hematoxylin and by chlorzinciodide. Cellulose is com- 
pletely soluble in a fresh copper ammonia solution. 

SIEVE TUBES 

Sieve tubes are downward-conducting cells. They conduct 
downward proteid food material. This fact is easily demon- 
strated by adding iodine to a section containing sieve tubes, in 
which case the sieve tubes are turned yellow. 

Developing sieve tubes have all the parts common to a living 
cell; but when fully mature, however, the nucleus becomes 
disorganized, but a layer of protoplasm continues to line the 
cell wall. 

Sieve tubes (Plate 46, Fig. 1) are composed of a great number 
of superimposed cells with perforated end walls and with non- 
porous cellulose side walls. The end walls of two adjoining 
cells are greatly thickened and the pores pass through both 



PLATE 46 





1. Longitudinal section of sieve tube {Cucurbita pepo, L.). 

2. Cross-section of sieve tube just above an end wall — sieve plate. 



138 



HISTOLOGY OF MEDICINAL PLANTS 



walls. This thickened part of the porous end walls of two sieve 
cells is called the sieve plate, and it may be placed in an oblique 
or a horizontal position. 

In a longitudinal section the sieve tubes are seen to be 
slightly bulging at the sieve plate, and through the pores extend 
protoplasmic strands. The strands are united on the upper 
and lower side of the sieve plate to form the protoplasmic strands 
of the living sieve tubes and the callus, layers of dried plants. 
This callus is frequently yellowish in color, and in all cases is 
separated from the cell wall. In certain plants the sieve plate 
occurs on the side walls of the sieve tubes in contact with other 
sieve tubes. 

SIEVE PLATE 

Sieve plates on cross-section (Plate 46, Fig. 2) are polygonal 
in outline, and the pores are either round or angled. Large 
sieve tubes and sieve plates occur hi pumpkin stem; but, almost 
without exception, in drug plants the sieve tubes are small 
and the sieve plate is inconspicuous. When the drug is pow- 
dered, the sieve tubes break up into undiagnostic fragments. 
When studying sections of the plants, the extent, size, and 
arrangement of the sieve tubes must always be noted. 

MEDULLARY BUNDLES, RAYS, AND CELLS 
Function 

The medullary ray cells are the lateral conducting cells of 
the plant. They conduct outwardly the water and inorganic 
salts brought up from the roots by the vessels and tracheids; 
and they conduct inwardly toward the centre of the stem the 
food material manufactured in the leaves and brought down by 
the sieve cells. The medullary rays thus distribute the in- 
organic and organic food to the living cells of the plant, and 
they conduct the reserve food material to the storage cells, and, 
lastly, they function in certain plants as storage cells. 

Occurrence 

The form, size, wall structure, and the distribution of the 
medullary ray bundles, rays, and cells are best ascertained by 



CONDUCTING TISSUE 



139 



studying: first, the cross-section of the plant; secondly, the 
radial section; and, thirdly, the tangential section. 

Students should be careful to distinguish between the medul- 
lary ray bundle, the medullary ray, and the meduUary ray cell. 
In some plants the bundles are only one cell wide, but in other 
plants the medullary ray bundle is more than one cell wide, 
frequently several cells wide. 

THE MEDULLARY RAY BUNDLE 

The medullary ray bundle is made up of a great many medul- 
lary ray cells. These bundles (Plate 106, Fig. 5) are of variable 
length, height, and width. The bundles are isolated, and they 
occur among and separate the other cells of the plants in which 
they occur. Tangential sections show the medullary ray 
bundle in cross-section. Such sections are lens-shaped, and 
they show both the width and the height of the medullary ray 
bundle. The length of the medullar^ ray bundle is shown in 
cross-sections. 

THE MEDULLARY RAY 

The medullary ray (Plate 47) is a term used to indicate 
that part of a medullary ray bundle which is seen in cross- 
sections and in radial sections. In cross-sections the length 
of the ray will be as great as the length of the bundle, and the 
width of the ray will be as great as the width of the medullary 
ray bundle at the point cut across. In longitudinal sections the 
medullary ray will differ in height according to the thickness of 
the bundle at the point cut. 

When the medullary rays extend from the centre of the stem 
to the middle bark, they are termed primary medullary rays; 
when they extend from the cambium circle to the middle bark, 
they are termed secondary medullary rays. As the plant grows, 
the diameter of the organ becomes greater and the number of 
medullary rays are increased. In each of these cases the medul- 
lary rays may be one or more than one cell wide, according to 
whether the medullary ray bundle is one or more than one cell 
wide. Even in the same plant the width of the medullary rays 
will vary if the bundle is more than one cell wide, according to 
width of the medullary ray bundle at the point cut across. 



CONDUCTING TISSUE 



141 



On cross-section the medullary rays are seen to vary greatly. 
In many plants they are more or less straight radial lines, as 
in quassia (Plate 105, Fig. 2); while in other plants they form 
wavy lines where they bend or curve around the conducting 
cells, as in piper methysticum, kava-kava (Plate 48, Fig. A). 

In the study of powdered drugs the radial view of the medul- 
lary rays is most frequently seen. 

In a perfect radial section (Plate 107, Fig. 2) the medullary 
rays are seen as tiers of cells in contact throughout their long 
diameter, and they run at right angles to the long diameter of 
the other cells. This view of the rays shows the length and 
height of the medullary ray. In logwood the rays are often 
forty cells high. In powdered barks, woods (Plate 47), and 
woody roots the radial View of the medullary rays is frequently 
diagnostic. 

In guaiacum officianale wood the medullary rays are one 
cell wide on cross-section, and up to six cells high on the tan- 
gential section. In santalum album the rays are from one to 
three cells wide on cross-section, and up to six cells high on 
tangential section. In the greater number of plants the rays 
are more than one cell wide. 

THE MEDULLARY RAY CELL 

The medullary ray cell (Plate 48, Fig. 1) is one of the in- 
dividual cells making up the medullary ray bundle and the 
medullary ray. 

The cross-sections of the cells which are seen in tangential 
sections show the cells to be mostly circular in outline when 
they occur in the central portion of medullary ray bundles of 
more than two cells in width; but they are more irregular in 
outline when the medullary ray bundle is only one cell wide. 
Even the cells of the three or more cell-wide bundles have ir- 
regular, outlined cells at the ends of the bundle and on the sides 
in contact with the other tissues. 

The length and height of the medullary ray cell are shown 
in radial sections; while the width and length of the medullary 
ray cells are shown in cross-sections. 



142 



HISTOLOGY OF MEDICINAL PLANTS 



Structure of Cells 

The structure of the individual cells forming the medullary 
rays differs greatly in different plants, but- is more or less con- 
stant in structure in a given species. 

The medullary rays of the wood usually have strongly pitted 
side and end walls, while the medullary rays of most barks are 
not at all, or only slightly, pitted. In most plants the cells are 
of nearly uniform size. Frequently, however, the cells vary in 
size in a given ray, as shown in the cross-section of kava-kava. 

Arrangement of the Cells in a Ray 

The union of any two cells in a ray is also of importance. 
In quassia the medullary ray cells have oblique end walls, so 
that on cross-section, the line of union between two cells is an 
oblique wall. In most plants the medullary ray cells have 
blunt or square or oblique end walls, so that the line of union 
is a straight line. 

In most plants the cells are much longer than broad, but the 
cells of sassafras bark are nearly as broad as long. 

The walls of the cortical medullary ray cells and the medul- 
lary rays of most roots and stems of herbs are composed of cellu- 
lose; while the walls of medullary ray cells occurring in woods 
are frequently lignified. 

There is a great variation in the character of the cell con- 
tents of medullary rays. In white pine bark (Plate 48, Fig. 
Bi) are deposits of tannin; in quassia wood, starch; in canella 
alba, rosette crystals of calcium oxalate, etc. 

LATEX TUBES 

Living latex tubes, like sieve tubes, have a layer of proto- 
plasm lining the walls, and, in addition, have numerous nuclei. 
In drug plants the nuclei are not distinguishable, but the proto- 
plasm is always clearly discernible. 

Latex tubes function both as storage and as conducting cells. 
They, like the sieve tubes, contain proteid substances chiefly, 
yet frequently starch is found. The cells bordering the latex 
tubes absorb from them, as needed, the soluble food material. 
While our knowledge concerning the function of latex in some 



PLATE 48 




A. Cross-section of kava-kava root (Piper methysticum, Forst., f.). 

1. Unequal diameter medullary ray cells. 

2. Vessels. 

3. Wood parenchyma. 

4. Wood fibres. 

B. Cross-section of white pine bark (Pinus strobus, L.). 

1. Wavy medullary rays with tannin. 

2. Parenchyma cells. 

3. Sieve cells. 



144 



HISTOLOGY OF MEDICINAL PLANTS 



plants is meagre, still in other plants it is practically certain 
that the latex is composed of nutritive substances which are 
utilized by the plant as food. In certain other plants the latex 
appears to be used as a means of resisting insect attacks and as 
a protection against injury. 

There are two types of latex tubes common to plants, namely, 
latex cells and latex vessels. Latex tubes developing from a 
single cell do not differ materially from a latex tube originating 
from the fusion of several cells. In each case the latex tube 
branches to such an extent that it bears no resemblance to or- 
dinary cells. It would seem that the ultimate branches are formed 
and develop in much the same manner as root hairs — that is, 
by a growing tip of the branch. A mature plant may therefore 
have latex tubes with almost numberless branches (Plate 50, 
Fig. 1) and be of very great length. 

The branches of latex tubes develop in such an irregular 
manner that it is possible to obtain a cross and a longitudinal 
section of the latex tubes by making a cross-section of stem. 
Such a section is shown in the drawing of the cross-section of 
the rhizome of black Indian hemp (Plate 49, Fig. B). 

The color of the latex in medicinal plants varies from a 
gray white in papaw (carica papaya), aromatic sumac, black 
Indian hemp, and bitter root, to white in the opium poppy, 
light orange in celandine, and deep orange in bloodroot (Plate 
50, Fig. 2). In each of these cases it is the latex which yields 
the important medicinal products. 

PARENCHYMA 

The larger amount of plant tissue is composed of parenchyma 
cells. These cells vary from square to oblong, or they may be 
irregular and branched. The end walls are square or blunt, 
and the wall is composed of cellulose, with the exception of the 
wood parenchyma, which has lignified walls. 

There are seven characteristic types of parenchyma cells: 
(1) cortical parenchyma, (2) pith parenchyma, (3) wood par- 
enchyma, (4) leaf parenchyma, (5) aquatic plant parenchyma, 
(6) endosperm parenchyma, (7) phloem parenchyma. 

Parenchyma cells, cortical, pith, aquatic plant, leaf, flower, 



PLATE 49 




A. Cross-section of black Indian hemp (Apocynum cannabinum, L.). 

1. Longitudinal section of a latex tube. 

2. Cross-section of latex tube. 

3. Parenchyma. 

B. Cross-section of a part of black Indian hemp root. 

4. Cross-section of a large latex tube. 

5. Parenchyma. 



PLATE 50 




Latex Vessels 



1. Radial-longitudinal section of dandelion root (Taraxacum officinale, 
Weber). 

2. Cross-section of sanguinaria root {Sanguinaria canadensis, L.). 

3. Cross-section of dandelion root. 



CONDUCTING TISSUE 



147 



and endosperm, conduct in all directions — upward, downward, 
and laterally. The direction of conduction depends upon the 
needs of the different cells forming the plant. The fluids pass 
from the cell with an abundance of cell sap to the cell with less 
cell sap. In this wall all cells are provided with food. 

Parenchyma cells conduct water absorbed by the roots and 
soluble carbohydrate material chiefly. 

The walls of all the different types of parenchyma cells are 
composed of cellulose with the exception of the wood parenchyma 
cells, the walls of which are lignified. The end walls of non- 
branched parenchyma cells and the cell terminations of branched 
cells are very blunt. 

CORTICAL PARENCHYMA 

Cortical parenchyma (Plate 51) differs greatly in size, thick- 
ness of the walls, and arrangement. A study of the longitudinal 
sections of different parts of medicinal plants reveals the fact 
that the cortical parenchyma cells form superimposed layers 
in which the end walls are either parallel, in which case the 
arrangement resembles that of several rows of boxes standing 
on end, or the end walls of the cells alternate with each other, 
in which case the arrangement is similar to that of the arrange- 
ment of the bricks in a building. 

In certain plants the cortical parenchyma cells are long and 
narrow and rectangular in shape, while in other plants the cells, 
although still rectangular in outline, are very broad and ap- 
proach the square form. 

All typical cortical parenchyma cells have uniformly thick- 
ened non-pitted walls. In most barks the parenchyma cells 
beneath the bark are elongated tangentially, but are very narrow 
radially. The cells are always arranged around intercellular 
spaces, which vary from triangular, quadrangular, etc., accord- 
ing to the number of cells bordering the intercellular space. 

PITH PARENCHYMA 

Pith parenchyma (Plate 52) differs from cortical parenchyma 
cells chiefly in the character of the walls, which are usually thicker 
and always pitted. 



PLATE 51 




Parenchyma Cells 
1. Longitudinal section of the cortical parenchyma of celandine root 
(Chelidonium majus, L.) 2. Cross-section of the cortical parenchyma of 
sarsaparilla root {Smilax officinalis, Kunth). 



PLATE 52 





A. Longitudinal section of the pith parenchyma of grindelia stem (Grin- 
delia squarrosa, [Pursh] Dunal). 

1. Cell cavity. 

2. Cross-section of the porous end wall. 

3. Surface view of the porous side wall. 

B. Cross-section of the pith parenchyma of grindelia stem. 

1. Cell cavity. 

2. Porous walls. 

3. Pitted end walls 



150 



HISTOLOGY OF MEDICINAL PLANTS 



LEAF PARENCHYMA 

The parenchyma cells (Plate 109, Fig. 1) of leaves, of flower 
petals, and the parenchyma cells of some - aquatic plants are 
branched; that is, each cell has more than two cell terminations. 
These cell terminations are frequently quite attenuated and 
usually very blunt. Such a cell structure provides for a greater 
amount of intercellular space and a maximum exposure of sur- 
face. This arrangement makes it possible for the parenchyma 
cells of the leaf to absorb more readily the enormous amount 
of carbon dioxide needed in the photosynthetic process. 

AQUATIC PLANT PARENCHYMA 

The parenchyma of aquatic plants (Plate 59) has large 
intercellular spaces jormed by the chains of cells. 

WOOD PARENCHYMA 

Wood parenchyma (Plate 105, Fig. 3) cells are the narrowest 
parenchyma cells occuring in the plant. Their walls are always 
lignified and strongly pitted, and in some cases the end walls 
common to two cells are obliquely placed. 

PHLOEM PARENCHYMA 

Phloem parenchyma (Plate 100, Fig. 8) cells are usually 
associated with sieve cells. They are very long, narrow, and 
have thin, non-pitted walls. The thinness of the walls un- 
doubtedly enables the cells to conduct diffusible food substance 
more quickly than the cortical parenchyma cells. 

PALISADE PARENCHYMA 

Palisade parenchyma of leaves is of the typical parenchyma 
shape and the end walls are placed nearly on a plane, even 
when more than one layer is present. The cells are verv small, 
however, and the walls are very thin and non-pitted. 



CHAPTER VI 



AERATING TISSUE 

The aerating tissue of the plant performs a threefold func- 
tion: first, it permits the exchange of gases during photo- 
synthesis; secondly, it permits the entrance of oxygen and the 
exit of carbon dioxide during respiration; and, thirdly, it permits 
the exit of the excess of water absorbed by the plant. 

The above functions are carried on by the stomata, the 
water-pores, the lenticels, and the intercellular spaces of the 
plant. The stoma functions as the chief channel for the passage 
of C0 2 -laden air into the leaf and of oxygen-laden air from the 
leaf to the atmosphere. The stoma also functions as an organ 
of transpiration, since through the stoma a large part of the 
excess water of the plant passes off into the air. 

WATER-PORES 

In certain plants the primary epidermis is provided with 
openings resembling stomata, but unlike stomata the orifice 
remains open, and instead of being located on the upper or 
lower surface of the leaf, they are located on the margin of 
leaves immediately outward from the veins. Water is given 
off to the atmosphere from these openings. Such an opening 
is usually designated as a water-pore. 

STOMATA 

The chief external openings of the epidermis of leaves, of 
herbs, and of young wood stems are known as stomata. Sur- 
rounding the stoma are two cells known as guard cells. 

Guard cells differ greatly in form, in size, in arrangement, 
in occurrence, in association, in abundance (Plates 53, 54, and 
55), and in color. The guard cells surrounding the stoma vary 
in form from circular to lens-shaped. In most leaves the outline 

151 



PLATE 53 




1. Stoma and surrounding cells of aconite stem (Aconitum napellus, L.). 

2. Stoma and angled striated walled surrounding cells of peppermint stem 
{Mentha piperita, L.). 3. Stoma and elongated surrounding cells of lobelia 
stem {Lobelia inflata, L.). 



PLATE 54 




Types of Stoma 



1. Under epidermis of short buchu (Barosma betulina, [Berg.] Bartlingand 
Wendl., f.) showing stoma and deposits of hesperidin. 

2. Under epidermis of Alexandria senna (Cassia acutifolia, Delile) showing 
stoma and thick-angled walled surrounding cells. 

3. Upper epidermis of eucalyptus leaf (Eucalyptus globulus, Labill.) show- 
ing sunken stoma and slightly beaded walled surrounding cells. 

4. Under epidermis of belladonna leaf (Atropa belladonna, L.) showing 
stoma and wavy, striated, walled epidermal cells. 



154 



HISTOLOGY OF MEDICINAL PLANTS 



of the guard cells is rounded or has a curved outline; but in a 
few cases the guard cells have angled outlines. 

The arrangement of the surrounding cells of the stoma 
is one of the most important characteristics of the different 
leaves. As a rule the number of surrounding cells about a 
stoma is constant for a given species. In senna leaves (Plate 
54, Fig. 2) there are normally two surrounding cells about 
each guard cell, while in coca there are four (Plate 55, Fig. 1). 
In senna the long diameter of the surrounding cells is parallel to 
the long diameter of the guard cells ; but in coca the long diameter 
of two surrounding cells is at right angles to the long diameter of 
the guard cells, while two cells are parallel to the long diameter 
of the guard cells. 

In most leaves cthere are more than two cells around the 
guard cells. 

The form and size of the surrounding cells must always be 
considered. In most leaves they are variable in size and form. 

Guard cells occur first, even with the surface of the leaf (Plate 
56, Fig. A); secondly, above the surface of the leaf (Plate 56, 
Fig. B) ; and, thirdly, below the surface of the leaf. (Plate 56, 
Fig. C). Only one of the above types occurs in a given species 
of plant. That is, plants with stomata above the surface of the 
leaf do not have stomata on a level with or below the leaf 
surface. 

The number of stomata on a given surface of a different leaf 
varies considerably. 

In many of the medicinal leaves stomata occur only on the 
under surface of the leaf. In other leaves stomata occur on both 
surfaces of the leaf ; but in such cases there are a greater number 
on the under surface. 

In certain leaves the long diameter of the guard cells is 
parallel to the length of the leaf ; in other cases the long diameter 
of the stoma is arranged at right angles to the length of the leaf. 

In other leaves the arrangement is still more irregular, the 
guard cells assuming all sorts of positions in relation to the 
length of the leaf. 

The relation of the stoma to surrounding cells is best shown 
in cross-sections of the leaf. In powders the relationship of 
the stoma to the surrounding cells is, however, readily ascer- 



PLATE 55 




Leaf Epidermi with Stoma 



1. Under epidermis of coca leaf {Erytliroxylon coca, Lam.) with stoma on 
a level with the surface. 

2. Under epidermis of false buchu (Marrubium peregrinum, L.) with stoma 
below the level of the surface. 

3. Upper epidermis of deer tongue (Trilisia odoratissima, [Walt.] Cass.) 
with stoma above the leaf surface. 



PLATE 56 




A. Cross-section of belladonna leaf (Atropa belladonna, L.). I, Epidermal 
cells; 2, Guard cells even with the leaf surface; 3, Surrounding cells; 4, Air 
space below the guard cells; 5, Palisade cells; 6, Mesophyll cells. B. Cross- 
section of deer tongue leaf. 1, Epidermal cells; 2, Guard cells above the sur- 
face of the leaf; 3, Surrounding cells; 4, Air space below the guard cells; 
5, Hypodermal cells. C. Cross-section of white pine leaf (Pinus strobus, L.). 
1, Epidermal and hypodermal cells; 2, Guard cells below the leaf surface; 
3, Surrounding cells; 4, Air space below the guard cells; 5, Parenchyma cells 
with projecting inner walls. 



AERATING TISSUE 



157 



tained. If the guard cells come in focus first, they are above 
the surface; if the guard cells and the surrounding cells come 
in focus at the same time, the stomata are even with the sur- 
face; if the stomata come in focus after the surrounding cells, 
they are below the surface of the leaf. The relationship of 
the stoma to the surrounding cells should always be ascertained, 
not only in cross-sections of the leaf, but also in powders. 

There is the greatest possible variation in the size of guard 
cells. This fact must always be kept in mind when studying 
leaves. This variation in the size of the guard cells is clearly 
illustrated by coca, senna, and by deer's-tongue. In coca the 
stomata are very small; in senna they are larger; while in 
deer's-tongue the stomata are very large. 

The width and length of the stoma or opening between the 
guard cells are of a character which must not be overlooked. 
Generally speaking, those leaves which have large guard cells 
will have correspondingly large stomata. 

The guard cells usually contain chloroplasts showing various 
stages of decomposition. 

In bay-rum leaf the guard cells are of a bright reddish- 
brown color, but in most leaves the guard cells are colorless. 

LENTICELS 

Lenticels are small openings occurring in the bark of plants. 
The lenticels bear the same relationship to the stem that the 
stomata do to the leaves. Lenticels, like stomata, have a three- 
fold function — namely, exchange of gases in photosynthesis, 
in respiration, and the giving off of water. 

Lenticels are macroscopically as well as microscopically 
important. When unmagnified the lenticels are circular, lens- 
shaped, or irregular in outline. They are arranged in parallel 
longitudinal lines or parallel transverse lines, or they are ir- 
regularly scattered. The latter is the usual arrangement. In 
most cases they are elevated slightly above the surface of the 
bark. In root barks particularly the lenticels stand out promi- 
nently from the surface of the bark and in many cases appear 
stalked. 

The color of the lenticels differs greatly in the different 



158 



HISTOLOGY OP MEDICINAL PLANTS 



plants. In acer spicatium they are brown; in witch-hazel they 
are gray; in xanthoxylium they are yellowish; and lastly, the 
number of lenticels occurring in a given surface of the bark 
should always be considered. 

On cross-sections the lenticel (Plate 57, Fig. 2) is seen to 
have a central depressed portion made up of loosely arranged 
cells. Bordering the cavity are typical cork cells. The cork 
cells immediately surrounding the lenticels are usually darker 
in color, and many of the cells are partly broken down. 

The size of lenticels will vary according to the type of the 
lenticel. In studying sections more attention should be paid 
to the character of the cells forming the lenticels than to the 
size of the lenticel. 

On cross-section the intercellular spaces (Plate 58) are tri- 
angular, quadrangular, or irregular. The spaces between equal 
diameter parenchyma cells is triangular if three cells surround 
the space, and quadrangular if four cells surround the space, 
etc. These spaces are in direct contact with similar spaces that 
traverse the tissue at right angles to its long axis. 

The branched mesophyll cells of the leaf and aquatic plant 
parenchyma (Plate 59) are arranged around irregular cavities. 
In leaves and aquatic plants these spaces run parallel to the 
long axis of the organ. 

In each of the above cases the cavity is formed by the sepa- 
ration of the cell walls. There is still another type of irregular 
cavities which is formed by the dissolution or tearing apart of 
the cell walls. Such cavities are found in the stems and roots 
of many herbs. 

The pith cells in the stems of many herbs become torn 
apart during the growth of the stem, with the result that large 
irregular cavities are formed. These cavities are usually filled 
with circulatory air. 

In the stems of conium, cicuta, angelica, and other larger 
herbaceous stems the pith separates into layers. When a 
longitudinal section is made of such a stem it is seen to be com- 
posed of alternating air spaces and masses of pith parenchyma. 

The intercellular spaces are very large in leaves where 
enormous quantities of carbon dioxide are vitalized in photo- 
synthesis. 



PLATE 58 




Intercellular Air Spaces 

A. Cross-section of uva-ursi leaf (Arctostaphylos uva-ursi, [L.] Spreng.). 
1. Irregular intercellular air spaces. 

B. Cross-section of the cortical parenchyma of sarsaparilla root {Smilax 
officinalis , Kunth) . 1, Triangular intercellular spaces; 2, Quadrangular in- 
tercellular air spaces; 3, Pentagular intercellular air spaces. 



PLATE-- 59 




Irregular Intercellular Air Spaces 

1. Skunk-cabbage (Symplocarpus foetidus, [L.] Nutt.) 

2. Calamus rhizome (Acorus calamus, L.). 



162 



HISTOLOGY OF MEDICINAL PLANTS 



In the rhizome of calamus and other aquatic plants the 
intercellular spaces are very large. The cells of these plants 
are arranged in the form of branching chains- of cells which thus 
provide for large intercellular spaces. 

The cells of the middle layer of flower petals, like the meso- 
phyll of leaves, is loosely arranged owing to the peculiar branch- 
ing form of the cells. 

Seeds and fruits contain, as a rule, few or no intercellular 
spaces. 



CHAPTER VII 



SYNTHETIC TISSUE 

Under synthetic tissue are grouped all tissues and cells which 
form substances or compounds other than protoplasm. Such 
compounds are stored either in special cavities or in the cells 
of the plant, as the glandular hairs; internal secreting cavities 
of barks, stems, leaves, fruits, seeds, and flowers; photosyn- 
thetic cells or cells with chlorophyll, and the parenchymatic 
cells which form starch, sugar, fats, alkaloids, etc. 

PHOTOSYTTTHETIC TISSUE 

The most important non-glandular synthetic tissue is the 
photosynthetic tissue, which is composed of the chlorophyll- 
bearing cells of the plant. These are the so-called green cells 
of leaves, of stems of herbs, of young woody stems, and in the 
older woody stems of plants like wild cherry, birch, etc. The 
greater part of the tissue of leaves is composed of chlorophyll- 
bearing cells. 

Leaves collectively constitute the greatest synthetic manu- 
facturing plant in the world, because the green cells of the leaf 
produce most of the food of men and animals. The two com- 
pounds utilized in the manufacture of food are carbon dioxide 
(C0 2 ) and water (H 2 0). These two compounds are combined 
by chlorophyll through the agency of light into starch. Chemi- 
cally this reaction may be expressed as follows : 

6C0 2 + 5 H 2 = 2C 6 H 10 O 5 + 60 2 . 

During the day a large quantity of starch is formed. At 
night through the action of a ferment the excess of starch remain- 
ing in the leaf is converted into sugar (C 6 Hi 2 6 ) — C c H 10 O 5 + 
H 2 = C 6 Hi 2 6 . In this form it is distributed to the living 
cells of the plant. The presence or absence of starch in leaves 
is easily ascertained by placing the leaf in hot alcohol to remove 

163 



164 



HISTOLOGY OF MEDICINAL PLANTS 



the chlorophyll, and by adding Lugol's solution. If starch is 
present, the contents of the cells will become bluish black; but 
if no starch is Dresent, the cells remain colorless. 

GLANDULAR TISSUE 

The glandular tissue of the plant is divided into two groups, 
according to where it occurs. These groups are, first, external 
glandular tissue, and secondly, internal glandular tissue. The 
most important external glandular tissue is composed of the 
glandular hairs. These are divided into two groups: first, 
unicellular; and secondly, multicellular glandular hairs. 

UNICELLULAR GLANDULAR HAIRS 

The unicellular glandular hairs are either sessile or stalked. 
Sessile unicellular hairs occur in digitalis leaves. 
Stalked unicellular hairs of digitalis are shown on Plate 60, 
Fig. 2. 

Unicellular uniseriate stalked glandular hairs occur on the 
stems of the common house geranium (Plate 61, Fig. 2), on the 
leaves of butternut, the leaves and stems of marrubium peregri- 
num (Plate 98, Fig. 5), and in arnica flowers. The stalk varies 
from two to ten cells; in eriodictyon the cells vary from four 
to eight cells. 

Unicellular multiseriate stalked glandular hairs are not of 
common occurrence. 

MULTICELLULAR GLANDULAR HAIRS 

Multicellular glandular hairs are divided into two groups: 
first, sessile; and secondly, stalked hairs. 

Multicellular sessile glandular hairs occur on the leaves of 
peppermint (Plate 60, Fig. 3), horehound (Plate 97, Fig. 7), 
and in hops (Plate 60, Fig. 4). In each of these hairs there are 
eight secretion cells. 

Stalked glandular hairs are divided into two groups: first, 
uniseriate stalked; and secondly, multiseriate stalked glandular 
hairs. 

Multicellular uniseriate stalked glandular hairs occur on 
the leaves of tobacco (Plate 61, Fig. 4), belladonna (Plate 61, 



PLATE 60 




Glandular Hairs 

1. Kamala (Mallotus philippinensis , [Lam.] [Muell.] Arg.). 

2. Digitalis leaf (Digitalis purpurea, L.). 

3. Peppermint leaf (Mentha piperita, L.). 

4. Lupulin. 

5. Cannabis indica leaf (Cannabis saliva, L.). 



166 



HISTOLOGY OF MEDICINAL PLANTS 



Fig. i), and digitalis (Plate 60, Fig. 2), and of the fruit of rhus 
glabra. 

Multicellular multiseriate stalked glandular hairs occur on 
the stems and leaves of cannabis indica (Plate 60, Fig. 5). 

In the glandular hair of kamala (Plate 60, Fig. 1) the num- 
ber of secretion cells is variable and papillate in form, and the 
cuticle is separated from the secretion cells. 

In the glandular hair of hops the outer wall or cuticle is torn 
away from the secretion cells, and the cavity thus formed serves 
as a storage cavity. This distended cuticle of the hops shows 
the outline of the cells from which it was separated. 

^Jn the glandular hairs of the mints the secreted products 
(volatile oils) are stored between the secretion cells and the outer 
detached cuticle. This cuticle is elastic, and it becomes greatly 
distended as the volatile oil increases in amount. 

In many of the so-called glandular hairs, tobacco, belladonna 
geranium, etc., the synthetic products are retained in the glandu- 
lar cells, there being no special cavity for their storage. 

These hairs usually contain an abundance of chlorophyll. 

The division wall of multicellular glandular hairs may be 
vertical, as in the two-celled hair of digitalis (Plate 60, Fig. 2) ; 
as in horehound (Plate 97, Fig. 6), and as in peppermint (Plate 
60, Fig. 3); in this case there are eight cells, and they form a 
more or less flat plate of cells. 

In other hairs the division wall is horizontal; this produces 
a chain of superimposed secreting cells, as in some of the gland- 
ular hairs of belladonna leaf (Plate 61, Fig. 1), etc. 

In other hairs the division walls are both vertical and hori- 
zontal, as in tobacco (Plate 61, Fig. 4), henbane (Plate 61, Fig. 
3), belladonna (Plate 61, Fig. 1). 

Other characters to be kept in mind in studying glandular 
hairs are the following: Color of cell contents; size of the 
cells, whether uniform or variable; character of wall, whether 
smooth or rough. 

SECRETION CAVITIES 

Secretion cavities are divided into three groups, according 
to the nature of the origin of the cavity: first, schizogenous 
cavities, which originate by a separation of the walls of the 



PLATE 61 




Stalked Glandular Hairs 

1. Belladonna leaf (Atropa belladonna, L.). 

2. Geranium stem {Geranium maculatum, L.). 

3. Henbane leaf (Hyoscyamus niger, L.). 

4. Tobacco leaf (Nicotiana tabacum, L.). 



168 



HISTOLOGY OF MEDICINAL PLANTS 



secretion cells; secondly, lysigenous cavities, which arise by the 
dissolution of the walls of centrally located secretion cells; and 
thirdly, schizo-lysigenous cavities, which, originate schizogen- 
ously, but later become lysigenous owing to the dissolution of 
the outer layers of the secretion cells. 

SCHIZOGENOTJS CAVITIES 

Schizogenous cavities occur in white pine bark (Plate 62, 
Fig. B). The cells lining the cavity are mostly tangentially elon- 
gated, and the wall extends into the cavity in the form of a 
papillate projection. Immediately back from these cells are 
two u br three layers of cells which resemble cortical parenchyma 
cells, except that they are smaller and their walls are thinner. 

In white pine bark there is a single layer of thin-walled 
cells lining the cavity. Immediately surrounding the secretion 
cells is a single layer of thick- walled fibrous cells. 

In klip buchu (Plate 63, Fig. B), as in white pine leaf (Plate 
64, Fig. B), there is a single layer of thin- walled secretion cells 
which are surrounded on three sides with parenchyma cells and 
on the outer side by epidermal cells. 

LYSIGENOUS CAVITIES 

Lysigenous cavities occur on the rind of citrus fruits — bitter 
and sweet orange, lemon, grapefruit, lime, etc., and in the leaves 
of garden rue, etc. 

In bitter orange peel (Plate 64, Fig. A) the cavity is very 
large, and the cells bordering the cavity are broken and partially 
dissolved. The entire cells back of these are white, thin-walled, 
tangentially elongated cells. There is a great variation in the 
size of these cavities, the smaller cavities being the recently 
formed cavities. 

SCHIZO-LYSIGENOUS CAVITIES 

Schizo-lysigenous cavities are formed in white pine bark 
and many other plants owing to the increase in diameter of the 
stem. In such cases the walls of the secreting cells break down. 
The resulting cavity resembles lysigenous cavities. 

Unicellular secretion cavities occur in ginger, aloe, calamus, 
and in canella alba barb. 




A. Cross-section of calamus rhizome" (Acorus calamus, L.). I, Intercel- 
lular space; 2, Parenchyma cells; 3, Secretion cavity. B. Cross-section of 
white pine bark (Pinus strobus, L.). 1, Parenchyma; 2, Secretion cavity; 
3, Secretion cells. 



PLATE 63 




MACKS' 

f 




A. Cross-section of a portion of canella alba bark {Canella alba, Murr.). 
1. Excretion cavity. 

B. Cross-section of a portion of klip buchu leaf. 

1. Epidermal cells. 

2. Secretion cavity. 

3. Secretion cells. 



PLATE 64 




B 



A. Cross-section of bitter orange peel (Citrus aurantium, amara, L.). 
1, Internal secretion cavity formed by the dissolution of the walls of the central 
secreting cells; 2, Secretion cells. B. Cross-section of white pine leaf (Pinus 
strobus, L.). I, Epidermal and hypodermal cells; 2, Parenchyma cells with 
protuding inner walls; 3, Endodermis; 4, Secretion cavitv; 5, Secretion cells. 



172 



HISTOLOGY OP MEDICINAL PLANTS 



In calamus (Plate 62, Fig. A) the cavity is larger than the 
surrounding cells; it is rounded in outline, and it contains 
oleoresin. These cavities are in contact, with the ordinary 
parenchyma cells, from which they are easily distinguished by 
their larger size and rounded form. 

The unicellular oil cavity of canella alba (Plate 63, Fig. A) 
is rounded or oval in cross-section and is many times larger 
than the surrounding cells. The wall, which is very thick, is 
of a yellowish color. 

Secretion cavities vary greatly in form, according to the 
part of the plant in which they are found. In flower petals and 
leaves they are spherical; in barks they are usually elliptical; 
in umbelliferous fruits they are elongated and tube-like. 

Mucilage cavities are not of common occurrence in medicinal 
plants. They occur, however, in the stem and root bark of 
sassafras, the stem bark of slippery elm, the root of althea, etc. 



CHAPTER VIII 



STORAGE TISSUE 

Most drug plants contain storage products because they 
are collected at a period of the year when the plant is storing, 
or has stored, reserve products. These products are stored 
in a number of characteristic ways and in different types of 
tissue. 

The most important of the different types of storage tissue 
that occurs in plants are the storage cells, the storage cavities, 
and the storage walls. 

STORAGE CELLS 

Several different types of cells function as storage tissue. 
These cells, which are given in the order of their importance, 
are parenchyma, crystal cells, medullary rays, stone cells, wood 
fibres, bast fibres, and epidermal and hypodermal cells. 

CORTICAL PARENCHYMA 

Cortical parenchyma of biennial rhizomes, bulbs, roots, 
and the parenchyma of the endosperm of seeds store most of 
the reserve economic food products of the higher plants. 

Pith parenchyma of sarsaparilla root (Plate 65, Fig. 4) and 
the pith parenchyma of the rhizome of memspermun, like the 
pith parenchyma of most plants, function as storage cells. 

WOOD PARENCHYMA 

Wood parenchyma, particularly of the older wood, function 
as storage tissue. The wood parenchyma of quassia, like the 
wood parenchyma of most woods, contain stored products. In 
some cases the wood parenchyma contain starch, in others crys- 
tals, and in others coloring matter, etc. 

In many plants, however, the parenchyma cells contain 
crystals. The parenchyma cells of rhubarb contain rosette 

173 



PLATE 65 




1. Stone cells with starch of Ceylon cinnamon (Cinnamomum zeylanicum, 
Nees.). 2. Stone cells with solitary crystals of calumba root (Jateorhiza 
palmata, [Lam.] Miers). 3. Parenchyma cells, with starch of cascarilla bark 
(Croton eluteria, [L.] Benn.). 4. Cortical parenchyma with starch of sarsa- 
parilla root (Smilax officinalis, Kunth). 5. Cortical parenchyma, with starch 
of leptandra rhizome (Leptandra virginica, [L.] Nutt.). 6. Crystal cells, with 
solitary crystals of quebracho bark (Schlechtendal). 7. Bast fibre of black- 
berry root with starch (Rubus cuneifolius, Pursh.). 



PLATE 66 




Mucilage and Resin 

1. Cross-section of elm bark ( Ulmus fulva, Michaux) showing two cavities 
filled with partially swollen mucilage. 

2. Mucilage mass from sassafras stem bark (Sassafras variifolium, L.). 

3. Mucilage mass from elm bark. 

4. Resin mass from white pine bark (Pinus strobus, L.). 



176 



HISTOLOGY OF MEDICINAL PLANTS 



crystals, while the parenchyma cells of the cortex of sarsaparilla 
and false unicorn root contain bundles of raphides. In every case 
observed the raphides are surrounded by mucilage. This is true 
of squills, sarsaparilla, false unicorn, etc. When cells with 
raphides and mucilage are mounted in a mixture of alcohol, 
glycerine, and water, the mucilage first swells and finally dis- 
appears. 

STORAGE CAVITIES 

Particular attention should be given to storage cavities 

whenever they occur in plants, for the reason that they are 
usually filled with storage products, and for the added reason 
that storage cavities are not common to all plants. Storage 
cavities occur in roots, stems, leaves, flowers, fruits, and seeds. 

CRYSTAL CAVITIES 

Characteristic crystal cavities occur in many plants. Such 
a cavity containing a bundle of raphides is shown in the cross- 
section of skunk cabbage leaf (Plate 67). 

SECRETION CAVITIES 

In white pine bark there are a great number of secretion 
cavities which are partially or completely filled with oleoresin. 
In the cross-sections of white pine bark the secretion cavities 
are very conspicuous, and they vary greatly in size. This 
variation is due, first, to the age of the cavity, the more re- 
cently formed cavities being smaller; and secondly, to the 
nature of the section, which will be longer in longitudinal section, 
which will be through the length of the secretion cavity, and 
shorter on transverse section. Such a section shows the width 
of the secretion cavity. ' 

Characteristic mucilage cavities occur in sassafras root, stem 
bark, elm bark (Plate 66, Fig. 1), marshmallow root, etc. 
These cavities form a conspicuous feature of the cross-section 
of these plants. The presence or absence of mucilage cavities 
in a bark should be carefully noted. 

LATEX CAVITIES 

The latex tube cavities are characteristic in the plants in 
which they occur. These cavities as explained under latex 
tubes are very irregular in outline. 



PLATE 67 




178 



HISTOLOGY OF MEDICINAL PLANTS 



OIL CAVITY 

Canella alba contains an oil cavity resembling in form the 
mucilage cavity of elm bark. 

Secretion cavities occur in most of the umbelliferous fruits. 
For each fruit there is a more or less constant number of cavities. 
Anise has twenty or more, fennel usually has six cavities, and 
parsley has six cavities. 

In poison hemlock fruits there are no secretion cavities. In 
certain cases, however, the number of secretion cavities can 
be made to vary. This was proved by the author in the case 
of celery seed. He found that cultivated celery seed, from 
which stalks are grown, contains six oil cavities (Plate 122, 
FigLa), while wild celery seed (Plate 102, Fig. 1), grown for its 
medicinal value, always contains more than six cavities. Most 
of the wild celery seeds contain twelve cavities. 

Many leaves contain cavities for storing secreted products. 
Such storage cavities occur in fragrant goldenrod, buchu, thyme, 
savary, etc. 

The leaves in which such cavities occur are designated as 
pellucid-punctate leaves. Such leaves will, when held be- 
tween the eye and the source of light, exhibit numerous rounded 
translucent spots, or storage cavities. 

GLANDULAR HAIRS 

The glandular hair of peppermint (Plate 60, Fig. 3) and other 
mints consists of eight secretion cells, arranged around a central 
cavity and an outer wall which is free from the secretion cells. 
This outer wall becomes greatly distended when the secretion 
cells are active, and the space between the secretion cells and 
the wall serves as the storage place for the oil. When the mints 
are collected and dried, the oil remains in the storage cavity 
for a long time. 

STONE CELLS 

The stone cells of the different cinnamons (Plate 65, Fig. 1) 
store starch grains; these grains often completely fill the stone cells. 

The yellow stone cells of calumba root (Plate 65, Fig. 2) 
usually contain four prisms of calcium oxalate, which may be 
nearly uniform or very unequal in size. 



STORAGE TISSUE 



179 



BAST FIBRES 

The bast fibres of the different rubus species (Plate 65, 
Fig. 7) contain starch. The medullary rays of quassia (Plate 
107, Fig. 2) contain starch; while the medullary rays of canella 
alba contain rosette crystals. In a cross-section of canella alba 
(Plate 81, Fig. 3) the crystals form parallel radiating lines which, 
upon closer examination, are seen to be medullary rays, in each 
cell of which a crystal usually occurs. 

The epidermal and hypodermal cells of leaves serve as 
water-storage tissue. These cells usually appear empty in a 
section. 

The barks of many plants — i.e., quebracho, witch-hazel, 
cascara, frangula, the leaves of senna and coca, and the root 
of licorice — contain numerous crystals. These crystals occur in 
special storage cells — crystal cells (Plate 65, Fig. 6) — which 
usually form a completely enveloping layer around the bast 
fibres. These cells are usually the smallest cells of the plant 
in which they occur, and with but few exceptions each cell 
contains but a single crystal. 

The epidermal cells of senna leaves and the epidermal cells 
of mustard are rilled with mucilage; the walls even consist of 
mucilage. Such cells are always diagnostic in powders. 

STORAGE WALLS 

Storage walls (Plates 68 and 69) occur in colchicum seed, 
saw palmetto seed, areca nut, nux vomica, and Saint Ignatius's 
bean. In each of these seeds the walls are strongly and char- 
acteristically thickened and pitted. In no two plants are they 
alike, and in each plant they are important diagnostic characters. 

Storage cell walls consist of reserve cellulose, a form of 
cellulose which is rendered soluble by ferments, and utilized 
as food during the growth of the seed. Reserve cellulose is 
hard, bony, and of a waxy lustre when dry. Upon boiling in 
water the walls swell and become soft. 

The structure of the reserve cellulose varies greatly in the 
different seeds in which it occurs in the thickness of the walls 
and in the number and character of the pores. 



PLATE 68 




Reserve Cellulose 

1. Saw palmetto (Serenoa serrulata, [Michaux] Hook., f.). 

2. Areca nut (Areca catechu, L.). 

3. Colchicum seed (Colchicum autumnale, L.). 
2>-A. Porous side wall. 

2,-B. Cell cavity above the side wall. 



PLATE 69 




Reserve Cellulose 

1. Endosperm of nux vomica {Strychnos nux vomica, L.). 

2. Endosperm of St. Ignatia bean {Strychnos ignatii, Berg.). 



CHAPTER IX 



CELL CONTENTS 

The cell contents of the plant are divided into two groups: 
first, organic cell contents; and secondly, inorganic cell contents. 

The organic cell contents include plastids, starch grains, 
mucilage, inulin, sugar, hesperidin, alkaloids, glucocides, tannin, 
resin, and oils. 

CHLOROPHYLL 

The chloroplasts of the higher plants are green, and they 
vary somewhat in size, but they have a similar structure and 
form. 

Chloroplasts are mostly oval in longitudinal view and rounded 
in cross-section view. Each chlorophyll grain has an extremely 
thin outer wall, which encloses the protoplasmic substance, the 
green granules, a green pigment (chlorophyll), and a yellow 
pigment (xanthophyll) . Frequently the wall includes starch, 
oil drops, and protein crystals. 

Chloroplasts are arranged either in a regular peripheral 
manner along the walls, or they are diffused throughout the 
protoplast. 

The palisade cells of most leaves are packed with chlorophyll 
grains. In the mesophyll cells the chlorophyll grains are not 
so numerous, and they are arranged peripherally around the 
innermost part of the wall. 

Chloroplasts multiply by fission — that is, each chloroplast 
divides into two equal halves, each of which develops into a 
normal chloroplast. 

Chlorophyll occurs in the palisade, spongy parenchyma, and 
guard cells of the leaf; in the collenchyma and parenchyma of 
the cortex of the stems of herbs and of young woody stems, and, 
under certain conditions, in rhizomes and roots exposed to 
light. Almost without exception young seeds and fruits have 
chlorophyll. 

182 



CELL CONTENTS 



183 



In powdered leaves, stems, etc., the chlorophyll grains occur 
in the cells as greenish, more or less structureless masses. Yet 
cells with chlorophyll are readily distinguished from cells with 
other cell contents. In witch-hazel leaf the chlorophyll grains 
appear brownish in color. Powdered leaves and herbs are 
readily distinguished from bark, wood, root, and flower powders. 

Leaves and the stems of herbs are of a bright-green color. 
With the exception of the guard cells, the chloroplasts occur one 
or more layers below the epidermis; but, owing to the trans- 
lucent nature of the outer walls of these cells, the outer cells of 
leaves and stems appear green. 

Wild cherry, sweet birch, and, in fact, most trees witn smooth 
barks have chloroplasts in several of the outer layers of the 
cortical parenchyma. When the thin outer bark is removed 
from these plants, the underlying layers are seen to be of a 
bright-green color. 

LEUCOPLASTIDS 

Leucoplastids, or colorless plastids, occur in the underground 
portions of the plant; they may, when these organs in which 
they occur are exposed to light, change to chloroplastids. 

Leucoplasts are the builders of starch grains. They take 
the chemical substance starch and build or mould it into starch 
grains, storage starch, or reserve starch. 

Other characteristic chromoplasts found in plants are yellow 
and red. Yellow chromoplasts occur in carrot root and nas- 
turtium flower petals. Red plastids occur in the ripe fruit of 
capsicum. 

STARCH GRAINS 

The chemical substance starch (C 6 Hi O 5 ) is formed in chloro- 
plasts. The starch thus formed is removed from the chloro- 
plasts to other parts of the plant because it is the function of 
the chloroplasts to manufacture and not to store starch. 

The starch formed by the chloroplasts is acted upon by a 
ferment which adds one molecule of water to C 6 Hio0 5 , thus 
forming sugar C 6 Hi 2 6 . This sugar is readily soluble in the 



184 



HISTOLOGY OF MEDICINAL PLANTS 



cell sap, and is conducted to all parts of the plant. The sugar 
not utilized in cell metabolism is stored away in the form of 
reserve starch or starch grains by colorless plastids or amyloplasts. 

The amyloplasts change the sugar into starch by extracting 
a molecule of water. This structureless material (starch) is 
then formed by the amyloplast into starch grains having a 
definite and characteristic form and structure. 

Starch grains vary greatly in different species of plants, 
owing probably to the variation of the chemical composition, 
density, etc., of the protoplast, and to the environmental con- 
ditions under which the plant is growing. 

OCCURRENCE 

Starch grains are simple, compound, or aggregate. Simple 
starch grains may occur as isolated grains (Plates 70, 71, and 
72), or they may be associated as in cardamon seed, white pepper, 
cubeb, and grains of paradise, where the simple grains stick 
together in masses, having the outline of the cells in which they 
occur. These masses are known as aggregate starch. 

Aggregate starch (Plate 76) varies greatly in size, form, and 
in the nature of the starch grains forming the aggregations. 

Compound starch grains may be composed of two or more 
parts, and they are designated as 2, 3, 4, 5, etc., compound 
(Plate 75). 

The parts of a compound grain may be of equal size (Plate 
75, Fig. 4), or they may be of unequal size (Plate 75, Fig. 2). 

In most powders large numbers of the parts of the com- 
pound grains become separated. The part in contact with other 
grains shows plane surfaces, while the external part of the grain 
has a curved surface. There will be one plane and one curved 
surface if the grain is a half of a two-compound grain; two 
plane and one curved surface if the grain is a part of a three- 
compound grain, etc. 

The simple starch grains forming the aggregations become 
separated during the milling process and occur singly, so that 
in the drugs cited above the starch grains are solitary and 
aggregate. 

Many plants contain both simple and compound starch 
grains (Plate 74, Fig. 3). 



CELL CONTEXTS 



185 



In some forms — e.g., belladonna root (Plate 75, Fig. 2) the 
compound grains are more numerous; while in sanguinaria the 
simple grains are more numerous, etc. 

OUTLINE 

The outline of starch grains is made up of (1) rounded, (2) 
angled, and (3) rounded and angled surfaces. 

Starch grains with rounded surfaces may be either spherical, 
as in Plate 74, Fig. 3, or oblong or elongated, as in Plate 71, 
Fig. 1. 

Other starches with rounded surfaces are shown on Plates 
72 and 73. 

Angled outlined grains are common to cardamon seed, white 
pepper, cubebs, grains of paradise (Plate 76, Fig. 4), and to corn 
(Plate 70, Fig. 3). 

The outlines of all compound grains are made up partly of 
plane and partly of curved surfaces. 

SIZE 

The size (greatest diameter) of starch varies greatly even 
in the same species, but for each plant there is a normal variation. 

In spherical starch grains the size of the individual grains is 
invariable, but in elongated starch grains and in parts of com- 
pound grains the size will vary according to the part of the grain 
measured. In zedoary starch (Plate 71, Fig. 4), for instance, 
the size will vary according to whether the end, side, or surface 
of the starch grain is in focus. 

The parts of compound grains often vary greatly in size. 
Such a variation is shown in Plate 75, Fig. 2. 

HILLTM 

The hilum is the starting-point of the starch grain or the 
first part of the grain laid down by the amyloplast. The hilum 
will be central if formed in the middle of the amyloplast, and 
excentral if formed near the surface of the amyloplast. It 
has been shown that the developing starch grain with eccentric 
hilum usually extends the wall of the amyloplast if it does not 
actually break through the wall. Starch grains with excentral 
hilums are therefore longer than broad. 



PLATE 70 




Starch 

1. Calabar bean (Physostigma venenosum, Balfour). 

2. Marshmallow root (Althcea officinalis, L.). 

3. Field corn (Zea mays, L.). 



PLATE 71 




Starch 

1. Galanga root (Alpinia officinarum, Hance). 2. Kola nut (Cola vera, 
[K.] Schum.). 3. Geranium rhizome (Geranium maculatum, L.). 4. Zedoary 
root (Curcuma zedoaria, Rose.). 4-^4. Surface view of starch grain. 4-B. Side 
view of starch grain. 4-C End view of starch grain. 



188 



HISTOLOGY OF MEDICINAL PLANTS 



In central hilum starch grains the grain is laid down around 
the hilum in the form of concentric layers. These layers are 
of variable density. The dense layers are formed when plenty 
of sugar is available, and the less dense layers are formed when 
little sugar is available. The unequal density of the different 
layers gives the striated appearance characteristic of so many 
starch grains. 

In eccentric hilum starch grains the starch will be deposited 
in layers which are outside of and successively farther from the 
hilum. 

The term hilum has come to have a broader meaning than 
formerly. Hilum includes at the present time not only the 
starting-point of the starch grain, but the fissures which form 
in the grain upon drying. In all cases these fissures originate 
in the starting-point, hilum, and in some cases extend for some 
distance from it. The hilum, when excentral, may occur in 
the broad end of the grain, galanga, and geranium (Plate 71, 
Figs. 1 and 3), or in the narrow end of the grain, zedoary (Plate 
7 1 /Fig. 4). 

NATURE OF THE HILUM 

The hilum, whether central or excentral, may be rounded 
(Plate 75, Fig. 1); or simple cleft, which may be straight (Plate 
71, Fig. 1); or curved cleft (Plate 71, Fig. 2); or the hilum may 
be a multiple cleft (Plate 74, Fig. 3). 

In studying starches use cold water as the mounting medium, 
because in cold water the form and structure are best shown, 
and because there is no chemical action on the starch. On the 
other hand, the form and structure will vary considerably if 
the starch is mounted in hot water or in solutions of alkalies 
or acids. The hilum appears colorless when in sharp focus, and 
black when out of focus. 

Starch grains, when boiled with water, swell up and finally 
disintegrate to form starch paste. 

Starch paste turns blue upon the addition of a few drops of 
weak lugol solution. Upon heating, this blue solution is de- 
colorized, but the color reappears upon cooling. If a strong 
solution of lugol is used in testing, the color will be bluish black. 



PLATE 72 




Starch 

1. Orris root (Iris florentinia L.). 

2. Stillingea root (Stillingea sylvatica, L.). 

3. Calumba root (Jateorhiza palmata, [Lam.] Miers 



PLATE 73 




Starch 

1. Male fern (Dryopteris marginalis, [L.] A. Gray). 

2. African ginger {Zingiber officinalis, Rose.). 

3. Yellow dock (Rumex crispus, L.). 

4. Pleurisy root (Asclepias tuber vsa, L.). 



PLATE 74 




Starch 

1. Kava-kava {Piper methysticum, Forst., f.). 

2. Pokeroot (Phytolacca americana, L.). 

3. Rhubarb (Rheum officinale, Baill.). 



PLATE 75 




Starch Grains 

1. Bryonia (Bryonia alba, L.)- 

2. Belladonna root (Atropa belladonna, L.). 

3. Valerian root (Valeriana officinalis, L.). 

4. Colchicum root (Colchicum autumnale, L.). 



PLATE 76 




Starch Masses 



1. Aggregate starch of cardamon seed (Elettaria cardamomum, Maton). 

2. Aggregate starch of white pepper (Piper nigrum, L.). 

3. Aggregate starch of cubebs (Piper cubeba, L., f.). 

4. Aggregate starch of grains of paradise (Amomum meleguetta, Rose). 



194 



HISTOLOGY OF MEDICINAL PLANTS 



INULIN 

Inulin is the reserve carbohydrate material found in the 
plants of the composite family. 

The medicinal plants containing inulin are dandelion, chicory, 
elecampane, pyrethrum, and burdock. Plate 77, Figs. 1 and 2 
show masses of inulin in dandelion and pyrethrum. 

In these plants the inulin occurs in the form of irregular, 
structureless, grayish- white masses (Plate 77). In powdered 
drugs inulin occurs either in the parenchyma cell or as irregular 
isolated fragments of variable size and form. Inulin is structure- 
less and the inulin from one plant cannot be distinguished 
microscopically from the inulin of another plant. For this 
reason inulin has little or no diagnostic value. The presence 
or absence of inulin should always be noted, however, in examin- 
ing powdered drugs, because only a few drugs contain inulin. 

When cold water is added to a powder containing inulin it 
dissolves. Solution will take place more quickly, however, in 
hot water. Inulin occurs in the living plant in the form of cell 
sap. If fresh sections of the plant are placed in alcohol or 
glycerine, the inulin precipitates in the form of crystals. 

MUCILAGE 

Mucilage is of common occurrence in medicinal plants. 
Characteristic mucilage cavities rilled with mucilage occur in 
sassafras stem (Plate 66, Fig. 2), in elm bark (Plate 66, Fig. 1), 
in althea root, in the outer layer of mustard seed, and in the 
stem of cactus grandinorus. In addition, mucilage is found 
associated with raphides in the crystal cells of sarsaparilla, 
squill, false unicorn, and poly gona turn. 

When drugs containing mucilage are added to alcohol, 
glycerine, and water mixture, the mucilage swells slightly and 
becomes distinctly striated, but it will not dissolve for a long 
time. Refer to Plate 79, Fig. 6. 

Mucilage, when associated with raphides, swells and rapidly 
dissolves when added to alcohol, glycerine, and water mixture. 
The mucilage is, therefore, different from the mucilage found 
in mucilage cavities, because it is more readily soluble. 

In coarse-powdered bark and other mucilage containing 



PLATE 77 




Inulin {Inula helenium, L.) 

1. Inulin in the parenchyma cells of dandelion root. 

2. Inulin from Roman pyrethrum root (Anacyclus pyrethrum, [L.] D. C). 



196 



HISTOLOGY OF MEDICINAL PLANTS 



drugs the mucilage masses are mostly spherical or oval in outline 
(Plate 66, Figs. 2 and 3) the form being similar to the cavity 
in which the mass occurs. 

Acacia, tragacanth, and India gum consist of the dried 
mucilaginous excretions. 

HESPERIDIN 

Hesperidin occurs in the epidermal cells of short and long 
buchu. It is particularly characteristic in the epidermal cells 
of the dried leaves of short buchu. In these leaves the hesperidin 
occurs in masses which resemble rosette crystals (Plate 54, Fig. 1). 

Hesperidin is insoluble in glycerine, alcohol, and water, but 
it dissolves in alkali hydroxides, forming a yellowish solution. 

VOLATILE OILS 

Volatile oils occur in cinnamon stem bark, sassafras root 
bark, flowers of cloves, and in the fruits of allspice, anise, fennel, 
caraway, coriander, and cumin. 

In none of these cases is the volatile oil diagnostic, but its 
presence must always be determined. 

When a powdered drug containing a volatile oil is placed 
in alcohol, glycerine, and water mixture the volatile oil con- 
tained in the tissues will accumulate at the broken end of the 
cells in the form of rounded globules, while the volatile oil 
adhering to the surface of the fragments will dissolve in the 
mixture and float in the solution near the under side of the 
cover glass. Volatile oil is of little importance in histological 
work. 

TANNIN 

Tannin masses are usually red or reddish brown. Tannin 
occurs in cork cells, medullary rays of white pine bark (Plate 48, 
Fig. B) , stone cells, and in special tannin sacs. 

The stone cells of hemlock and tamarac bark and the medul- 
lary rays of white pine and hemlock bark contain tannin. 

Tannin associated with prisms occurs in tannin sacs in white 
pine and tamarac bark. These sacs are frequently several 
millimeters in length and contain a great number of crystals 
surrounded by tannin. 



CELL CONTENTS 



197 



Deposits of tannin are colored bluish black with a solution 
of ferric chloride. 

ALEURONE GRAINS 

Aleurone grains are small granules of variable structure, 
size, and form, and they are composed of reserve proteins. 
They occur in celery, fennel, coriander, and anise, fruits, in 
sesame, sunflower, curcas, castor oil, croton oil, bitter almond, 
and other oil seeds. 

In many of the seeds the aleurone grains completely fill the 
cells of the endosperm, embryo, and peristerm. In wheat, rye, 
barley, oats, and corn the aleurone grains occur only in the 
outer layer or layers of the endosperm, the remaining layers 
in these cases being filled with starch. 

In powdered drugs the aleurone grains occur in parenchyma 
cells or free in the field. 

STRUCTURE OF ALEURONE GRAINS 

Aleurone grains are very variable in structure. The simplest 
grains consist of an undifferentiated mass of proteid substance 
surrounded by a thin outer membrane. In other grains the 
proteid substance encloses one or more rounded denser proteid 
bodies known as globoids. In other grains a crystalloid— crystal- 
like proteid substance — is present in addition to the globoid. 
In some grains are crystals of calcium oxalate, which may occur 
as prisms or as rosettes. All the different parts, however, do 
not occur in any one grain. In castor-oil seed (Plate 77a, Fig. 8) 
are shown the membrane (^4), the ground mass (B), the crys- 
talloid (C), and the globoid (D). 

FORM OF ALEURONE GRAINS 

Much attention has been given to the study of the special 
parts of the aleurone grains, but one of the most important 
diagnostic characters has been overlooked, namely, that of 
comparative form. For the purposes of comparing the forms of 
different grains, they should be mounted in a medium in which 
the grain and its various parts are insoluble. Oil of cedar is 
such a medium. The variation in form and size of the aleurone 
grains when mounted in oil of cedar is shown in Plate 77a. 



198 



HISTOLOGY OF MEDICINAL PLANTS 



DESCRIPTION OF ALEURONE GRAINS 

The aleurone grains of curcas (Plate 77a, Fig. 1) vary in form 
from circular to lens-shaped, and each grain contains one or 
more globoids. The globoids are larger when they occur singly. 
In sunflower seed (Plate 77a, Fig. 2) the grains vary from reni- 
form to oval, and one or more globoids are present; many occur 
in the center of the grain. 

The aleurone grains of flaxseed (Plate 77a, Fig. 3) resemble 
in form those of sunflower seed, but the grains are uniformly 
larger and some of the grains contain as many as five 
globoids. 

In bitter almond (Plate 77a, Fig. 4) the aleurone grains are 
mostly circular, but a few are nearly lens-shaped. A few of 
the large, rounded grains contain as many as nine globoids; 
in such cases one of the globoids is likely to be larger than the 
others. The aleurone grains of cro ton-oil seed (Plate 77a, Fig. 5) 
are circular in outline, variable in form, and each grain contains 
from one to seven globoids. 

In sesame seed (Plate 77a, Fig. 6) the typical grain is angled 
in outline and the large globoid occurs in the narrow or con- 
stricted end. 

The aleurone grains of castor-oil seed (Plate 77a, Fig. 7) re- 
semble those of sesame seed, but they are much larger, and 
many of the grains contain three large globoids. When these 
grains are mounted in sodium-phosphate solution, the crystal- 
loid becomes visible. 

TESTS FOR ALEURONE GRAINS 

Aleurone grains are colored yellow with nitric acid and red 
with Millon's reagent. 

The proteid substance of the mass of the grain, of the globoid, 
and of the crystalloid, reacts differently with different reagents 
and dyes. 

The ground substance and the crystalloids are soluble in 
dilute alkali, while the globoids are insoluble in dilute alkali. 

The ground substance and crystalloids are soluble in sodium 
phosphate, while the globoids are insoluble in sodium phosphate. 

Calcium oxalate is insoluble in alkali and acetic acid, but 
it dissolves in hydrochloric acid. 



PLATE 77a 



9 



Q 



8 
B 





(5? 



1.0 



® 5© 

Aleurone Grains 

1. Curcas (Jatropha curcas, L.). 

2. Sunflower seed (Helianthus annuus, L.). 

3. Flaxseed {Linum usitatissimum, L.). 

4. Bitter almond (Prunus amygdalus, amara, D.C.). 

5. Croton-oil seed (Croton tiglium, L.). 

6. Sesame seed (Sesamum indicum, L.). 

7 and 8. Castor-oil seed (Ricinus communis, L.). 





1 &| 1 



200 



HISTOLOGY OF MEDICINAL PLANTS 



CRYSTALS 

Calcium oxalate crystals form one of the most important 
inorganic cell contents found in plants,, because of the per- 
manency of the crystals, and because the forms common to 
a given species are invariable. By means of calcium oxalate 
crystals it is possible to distinguish between different species. 
In butternut root bark, for instance, only rosette crystals are 
found, while in black walnut root bark — a common substitute 
for butternut bark — both prisms and rosettes occur. This is 
only one of the many examples which could be cited. 

These crystals, for purposes of study, will be grouped into 
four principal classes, depending upon form and not upon crystal 
system. These classes are micro-crystals, raphides, rosettes, 
and solitary crystals. 

MICRO-CRYSTALS 

Micro-crystals are the smallest of all the crystals. Under the 
high power of the microscope they appear as a V, a Y, an X, 
and as a T. They are, therefore, three- or four-angled (Plate 78). 
The thicker portions of these crystals are the parts usually 
seen, but when a close observation of the crystals is made the 
thin portions of the crystal connecting the thicker parts may 
also be observed. Micro-crystals should be studied with the 
diaphragm of the microscope nearly closed and with the high- 
power objective in position. While observing the micro-crystals, 
raise and lower the objective by the fine adjustment in order to 
bring out the structure of the crystal more clearly. Micro- 
crystals occur in parenchyma cells of belladonna, scopola, 
stramonium, and bittersweet leaves; in belladonna, in horse- 
nettle root, in scopola rhizome, in bittersweet stems, and in 
yellow and red cinchona bark, etc. 

The crystals in each of the above parts of the plant are similar 
in form, the only observed variation being that of size. Their 
presence or absence should always be noted when studying 
powders. 

RAPHIDES 

Raphides, which are usually seen in longitudinal view, re- 
semble double-pointed needles. They are circular in cross- 



PLATE 78 



4 



t> < 



2 «a 



^3 

^ 5 7 * 

4) ^> 



3 4 ^ 



V 



A 



^7 



V <7 A 



4> 



5 



1$> ^ ^ 



Micro-Crystals 

1. Horse-nettle root (Solatium carolinense, L.). 

2. Scopola rhizome {Scopola carniolica, Jacq.). 

3. Belladonna root {Atropa belladonna, L.). 

4. Bittersweet stem (Solanum dulcamara, L.). 

5. Scopola leaf (Scopola carniolica, Jacq.). 

6. Tobacco leaf (Nicotiana tabacum, L.). 

7. Belladonna leaf (Atropa belladonna, L.). 



202 



HISTOLOGY OF MEDICINAL PLANTS 



section, and the largest diametej is at the centre, from which 
they taper gradually toward either end to a sharp point. 

Raphides occur in bundles, as in false unicorn root (Plate 79, 
Figs. 6, A, B, and C), rarely as solitary crystals. 

In ipecac root the crystals are usually solitary. In sar- 
saparilla root, squill, etc., the raphides occur both in clusters, 
part of bundle, or in bundles, and as solitary crystals. 

In most drugs the crystals are entire; but in squills, where 
the raphides are very large, they are broken. In phytolacca 
(Plate 79, Fig. 1) and in hydrangea the raphides are usually 
broken, owing to the fact that these drugs contain large quan- 
tities of fibres which break them up into fragments when the 
drug is milled. 

There is the greatest possible variation in the size of raphides 
in the same and in different drugs, but the larger forms are 
constant in the same species. 

Raphides are deposited in parenchyma cells and in special 
raphides sacs. These crystals are always surrounded with 
mucilage. 

ROSETTE CRYSTALS 

Rosette crystals are compound crystals composed of an 
aggregation of small crystals arranged in a radiating manner 
around a central core. This core appears nearly black, and 
the whole mass is nearly spherical. The free ends of the crystals 
are sharp-pointed or blunt. 

Characteristic rosette crystals occur in frangula bark, spike- 
nard root, wahoo stem, root bark, rhubarb, etc. (Plate 80, 
Figs- 1, 2, 3, 4, 5, and 6). 

These crystals are very variable in size. This variation is 
illustrated by the crystals of Plate 80. 

Usually there is a variation in size of the crystals occurring 
in a given plant, but for each plant there is a more or less uni- 
form variation. For instance, the largest rosette crystal occur- 
ring in wahoo root bark (Plate 80, Fig. 5) is smaller than the 
largest crystal occurring in rhubarb (Plate 80, Fig. 6), etc. 

The prisms forming the rosette crystals, like all prisms, 
decompose white light, with the result that rosette crystals 
frequently appear variously colored. Rhubarb crystals, for 



PLATE 79 




Raphides 



i. Phytolacca root {Phytolacca americana, L.). 2. Squills (Urginea mari- 
tima [L.] Baker). 3. Hydrangea root {Hydrangea arborescens, L.). 4. Con- 
vallaria {Convallaria majalis, L.). 5. Carthagean ipecac {Cephcelis acuminata 
Karst.) 6. Bundle of raphides from false unicorn root. 

A. Bundle surrounded with mucilage. B. Mucilage expanded and par- 
tially dissolved. C. Bundle free of mucilage. 



PLATE 80 




Rosette Crystals 

1. Frangula bark {Rhamnus jrangula, L.)- 

2. White oak bark {Quercus alba, L.). 

3. Spikenard root {Aralia racemosa, L.). 

4. Wahoo stem bark {Euonymus atropurpureus, Jacq.). 

5. Wahoo root bark {Euonymus atropurpureus, Jacq.)- 

6. Rhubarb {Rheum officinale, Baill.). 



CELL CONTENTS 



205 



instance, are blue or violet. Most of the smaller rosette crystals, 
however, appear grayish white with a darker-colored centre. 

Rosette crystals occur in parenchyma cells (Plate 81, Fig. 4) 
and in medullary rays (Plate 81, Fig. 3). 

SOLITARY CRYSTALS 

Solitary crystals are the most variable of all the forms of 
calcium oxalate. They usually occur in crystal cells associated 
with bast fibres and stone cells, less frequently in stone cells 
(Plate 33, Fig. 2). There are many different and characteristic 
forms of prisms. The more common are: 

1. Rectangular: 

A. Parallelepipeds. 

B. Cubes. 

2. Polyhedrons: 

A. Irregular polyhedrons. 

I. Flat bases. 

(a) Non-notched. 

(b) Notched. 
II. Tapering bases. 

B. Octohedrons. 

The crystals occurring in Batavia cinnamon and henbane 
leaves are parallelopipeds (Plate 82, Figs. 1 and 2). 

The crystals occurring in cactus grandiflorus, hemlock bark, 
krameria root, and soap bark are irregular polyhedrons (Plate 
83). They are longer than broad, and the ends are tapering. 
The crystal of cactus grandiflorus has the narrowest diameter 
of these four, while the crystals of soap bark have the widest 
diameter. In coca leaf, xanthoxylum bark, elm bark, Spanish 
licorice, and in white oak (Plate 84), and in cocillina bark (Plate 
82, Fig. 4) the crystals are all irregular polyhedrons with flat 
bases. They are mostly longer than broad and they are all 
widest in the centre; in each a few crystals are notched, but 
most of the crystals are not notched. 

The crystals in quassia wood, uva-ursi leaf, and most of those 
of quebracho and wild cherry bark (Plate 86, Figs. 1,2,3, an d 4) 
are irregular polyhedrons with flat ends. They are longer than 
broad, widest at the centre, and non-notched. 

Cubes occur in senna, cascara sagrada, frangula, white pine, 



PLATE 81 




Inclosed Rosette Crystals 

1. Hops {Humulus lupulus, L.). 

2. Bracts of cannabis indica {Cannabis sativa, variety Indica, Lamarck). 

3. Medullary rays of canella alba. 

4. Parenchyma cells of mandrake (Podophyllum peltatum, L.). 



PLATE 82 




Solitary Crystal 

1. Batavia cinnamon (cinnamomum burmanni, Nees). 

2. Henbane leaves {Hyoscyamus niger, L.). 

3. Morea nutgalls. 

4. Cocillana bark {Guarea rusbyi [Britton], Rusby). 



PLATE 83 




PLATE 84 




Solitary Crystals 

1. Coca leaf {Erythroxylon coca, Lamarck). 

2. Xanthoxylum bark (Zanthoxylum americanum, Miller). 

3. Elm bark (Ulmus fulva, Michaux). 

4. Spanish licorice root (Glycyrrhiza glabra, L.). 

5. White oak bark (Quercus alba, L.). 



210 



HISTOLOGY OF MEDICINAL PLANTS 



tamarac (Plate 85), quassia, uva-ursi, quebracho, and in wild 
cherry (Plate 86). 

The crystals of morea nutgalls (Plate 82, Fig. 3) are octo- 
hedrons, and they resemble the crystals of calcium oxalate found 
in urinary sediments. 

While studying the prisms, focus first on the upper surface 
and then down to the under surface in order to observe the 
forms accurately. 

There are several plants in which more than one form of 
crystal occur. Rosette crystals and prisms are associated, for 
instance, in cascara sagrada, frangula, condurango, dogwood, 
and pleurisy root (Plate 87, Figs. 1, 2, 3, 4, and 5). 

An important factor to be kept in mind in studying crystals 
is the number — whether abundant, as in rhubarb, or sparingly 
present, as in mandrake, etc. Variation in the number of 
crystals is not uncommon, even in different parts of the same 
plants. In wahoo stem bark, for instance, there are several 
times as many rosette crystals as there are in the root bark. 

Crystals of calcium oxalate are freely soluble in dilute 
hydrochloric acid without effervescence; but they are insoluble 
in acetic acid and in sodium and potassium hydroxide solutions. 
With sulphuric acid they form crystals of calcium sulphate. 

CYSTOLITHS 

Cystoliths consist of calcium carbonate deposited over and 
around a framework of cellulose. 

FORMS OF CYSTOLITHS 

The forms of cystoliths differ greatly in the different plants 
in which they occur. 

In the rubber-plant leaf, the cystolith resembles a bunch of 
grapes and is stalked; in ruellia root (Plate 87, Fig. 1) the cysto- 
liths vary from nearly circular to narrowly cylindrical, and no 
stalk is present; also the cystolith nearly fills the cell in which 
it occurs. In the hair of cannabis indica (Plate 88, Fig. 3), the 
cystolith varies in form according to the size and shape of the 
hair, but in all the hairs the cystolith appears to be attached to 
the upper curved part of the inner wall of the hair. 



PLATE 85 





Solitary Crystals 

1. India senna (Cassia angustifolia, Vahl.). 

2. Cascara sagrada bark (Rhamnus purshiana, D. C). 

3. Frangula bark (Rhamnus f ran gula, L.). 

4. White pine bark (Pinus strobus, L.). 

5. Tamarac bark (Larix laricina [Du Roi], Koch). 



PLATE 86 




Solitary Crystals 



1. Quassia (Picrcena excelsa [Swartz.], Lindl.). 

2. Uva-ursi leaf (Arctostaphylos uva-ursi [L.], Spring.). 

3. Quebracho bark (Aspidosperma quebracho-bianco, Schlechtendal). 

4. Wild-cherry bark (Prunus serotina, Ehrh.). 



PLATE 87 




Rosette Crystals and Solitary Crystals Occurring in 

1. Cascara sagrada bark (Rhamnus purshiana, D.C.). 

2. Frangula bark (Rhamnus frangula, L.). 

3. Cundurango bark (Marsdenia cundurango t [Triana] Nichols). 

4. Dogwood root bark (Cornus florida, L.). 

5. Pleurisy root (Asclepias tuberosa, L.). 



PLATE 88 




Cystoliths 



1. Ruellia root (Ruellia ciliosa, Pursh.). 

2. Pellionia leaf. 

3. Cannabis indica (Cannabis sativa, variety Indica, Lam.) 



CELL CONTENTS 



215 



Cystoliths occur, then, in special cavities, in parenchyma 
cells (rubber-plant leaf, fig, pellionea, and mulberry), and in 
non-glandular hairs (cannabis indica). 

In powdered ruellia root the cystoliths occur in or are sepa- 
rated from the parenchyma cells. 

TESTS FOR CYSTOLITHS 

When dilute hydrochloric acid or acetic acid is added to 
cystoliths a brisk effervescence takes place with the evolution 
of carbon dioxide gas. 



j 



Part III 



HISTOLOGY OF ROOTS, RHIZOMES, STEMS, 
BARKS, WOODS, FLOWERS, FRUITS, 
AND SEEDS 

In Part II the different types of cells and cell contents found 
in plants have been studied. In Part III it will be shown how 
these different cells are associated and the nature of the cell 
contents in the different parts of the plant. These parts are 
the root, the rhizome, the stem of herbs, bark and wood of 
woody stems, the leaf, the flower, the fruit, and the seed. 



CHAPTER I 



ROOTS AND RHIZOMES 

Some fifty-five roots, rhizomes, and rhizomes and roots are 
official in the pharmacopoeia and national formulary. About 
5 of these are obtained from monocotyledonous plants, and 
50 from dicotyledonous plants. 

In studying the structure of roots and rhizomes, then, it 
must first be determined whether the root in question is mono- 
cotyledonous or dicotyledonous. This fact is ascertained by 
determining the type of the fibro- vascular bundle. The bundle 
is of the open collateral type in all rhizomes and roots obtained 
from monocotyledonous plants, but it is closed, radial, or con- 
centric in the monocotyledonous type. 

In both of these groups the cellular plan of structure is 
similar, the chief variation being the absence of one or more 
types of cells, the variation in the amount, in arrangement, in 
the anatomical structure, in the color, and in the cell contents 
of the individual cells. These facts will be impressed on the 
mind while studying the rhizomes and the roots. 

CROSS-SECTION PINK ROOT 

The cross-section of pink root (Plate 89) has the following 
structure : 

Epidermis. The epidermal cells are small, nearly as long 
as broad, and the outer wall is thicker and darker in color than 
the side and inner walls. The cells usually contain air. 

Cortex. The cortical parenchyma cells are very large and 
somewhat rounded in outline, and the walls are white. There 
are about twelve rows of these cells, and each cell contains 
numerous small, rounded starch grains. 

Endodermis. The endodermal cells are tangentially elon- 
gated, and the walls are very thin and white. There are two 
or three layers of endodermal cells; the cells' outer layers are 
larger than the cells of the inner layers. 

219 



PLATE 89 




ROOTS AND RHIZOMES 



221 



Pericycle. The cells forming the pericycle are sieve cells 
and phloem parenchyma. The sieve cells are small, angled cells 
with extremely thin, white walls. 

The phloem parenchyma resemble the sieve cells, except 
that they are larger. 

Cambium. The cambium cells are rectangular in shape; 
the walls are thin and white. 

Xylem. The xylem is composed of tracheids, wood paren- 
chyma, and wood fibres. 

Tracheids. The tracheids are the largest diameter cells of 
the centre of the root. The walls are thick and the cells are 
slightly angled in outline. 

Wood Parenchyma. The wood parenchyma cells surrounding 
the tracheids are five to seven, angled, and the walls are not 
so thick as the walls of the tracheids. 

Medullary Rays. The medullary ray cells resemble the 
structure of the wood parenchyma cells, but they are radially 
elongated. 

Pith Parenchyma. The cells forming the pith parenchyma 
are larger than the cells of wood parenchyma, but their struc- 
ture is similar. 

CROSS-SECTION RTJELLIA ROOT 

The cross-section of ruellia root (Plate 90) shows the follow- 
ing structure. It should be carefully noted how the structure 
differs from that of pink root: 

Epidermis. The epidermal cells are angled and variable in 
size; many of the epidermal cells are modified as root hairs. 

Hypodermis. The cells of the hypodermis are one layer 
in thickness and their structure is similar to the epidermal 
cells. 

Cortex. The cortex contains parenchyma and stone cells. 
The outer layers of the cortical parenchyma cells are round in 
outline, and they contain dark-brown cell contents, while the 
cortical parenchyma cells bordering on the endodermis are small 
and they are free of dark-brown contents. 

Many of the inner parenchyma cells contain amorphous 
deposits of calcium carbonate. 



PLATE 90 




Ruellia Root {Ruellia ciliosa, Pursh.). 

1. Epidermis with root hair. 2. Parenchyma cells with dark contents. 
3. Sclerid. 4. Parenchyma without dark cell contents. 5. Endodermis. 
6. Bast fibers and phloem. 7. Cambium. 8. Xylem. 10. Pith. 



ROOTS AND RHIZOMES 



223 



The stone cells are porous and striated, and the walls are 
thick and white. 

Endodermis. The endodermal cells are tangentially elon- 
gated, and the walls are thin and white. 

Pericycle. The cells forming the pericycle are the sieve 
cells, bast fibres, and phloem parenchyma. 

The sieve cells are small, angled cells with thin, white walls. 

The phloem parenchyma cells resemble the sieve cells, but 
they are larger. 

The bast fibres occur singly or in groups of two or three. 
They are rounded in outline, and the walls are white, non- 
porous, and non-striated. 

Xylem. The xylem is composed of vessels, wood parenchyma, 
and wood fibres. 

Vessels. The vessels are rounded in outline and few in 
number. 

Wood Parenchyma. The wood parenchyma cells are variable 
in size and shape, but all the cells are angled in outline. 

Medullary Rays. The medullary ray cells are not clearly 
distinguishable. 

Pith Parenchyma. The pith parenchyma cells of the centre 
of the root resemble the cortical parenchyma cells. 

That the structure of rhizomes is similar to the structure of 
roots is shown by the drawings of spigelia rhizome (Plate 91), 
and by ruellia rhizome (Plate 92). 

CROSS-SECTION SPIGELIA RHIZOME 

The cross-section of spigelia rhizome (Plate 91) is as follows: 

Epidermis. The epidermal cells are nearly angled and free 
of cell contents. 

Cortex. The cortical parenchyma cells are usually slightly 
tangentially elongated. The cells of the outer layers are larger 
than the cells of the inner layers. 

Phloem. The phloem contains sieve cells and phloem 
parenchyma. The sieve cells are small, angled cells with thin, 
white walls. 

The phloem parenchyma cells resemble the sieve cells, but 
they are larger. 

Cambium. The cambium cells are rectangular, and they are 



PLATE 91 




Mil* 




mar ■ 



Cross-Section of Rhizome of Spigelia marylandica, L. 
Epidermis. 2. Cortical parenchyma. 3. Phloem. 4. Cambium. 
5. Xylem. 6. Internal phloem. 7. Pith with starch. 



PLATE 92 




Cross-Section of Rhizome of Ruellia ciliosa, Pursh. 
1. Epidermis. 2. Cystolith. 3. Stone cell. 4. Cortical parenchyma. 
5. Bast fibres. 6. Pericycle. 7. Xylem. 8. Pith. 



226 



HISTOLOGY OF MEDICINAL PLANTS 



usually not clearly seen because the walls are partially 
collapsed. 

Xylem. The xylem is composed of vessels, wood parenchyma, 
medullary rays, and pith parenchyma. 

Vessels. The vessels are slightly angled in outline and few 
in number. 

Wood Parenchyma. The wood parenchyma cells are small 
and angled. 

Medullary Rays. The medullary ray cells are tangentially 
elongated, but in structure resemble the wood parenchyma cells. 

Pith Parenchyma. The pith parenchyma cells are rounded 
in outline and contain small, simple, rounded starch grains. 

CROSS-SECTION RUELLIA RHIZOME 

The cross-section of ruellia rhizome (Plate 92) differs from 
the structure of spigelia rhizome. It is as follows: 

Epidermis. The epidermal cells vary in shape from nearly 
square to oblong, and they are rilled with dark-brown cell 
contents. 

Cortex. The cortex contains parenchyma and stone cells. 

The outer layer of the cortical parenchyma cells are variable 
in size and many of the cells contain deposits of calcium car- 
bonate and dark cell contents; the inner parenchyma cells are 
larger and they are free of the dark-brown cell contents, but 
many of the cells contain deposits of calcium carbonate. 

Stone cells with thick, white, porous, and striated walls occur 
in among the cortical parenchyma cells. 

Phloem. The phloem contains sieve cells, phloem, paren- 
chyma, and bast fibres. 

The sieve cells are small and with thin, white, angled walls. 

The phloem parenchyma cells resemble the sieve cells, but 
they are larger. 

The bast fibres occur singly or in groups of two or three. 
The walls are white, non-porous, and non-striated. 

Cambium. The cambium layer is composed of rectangularly 
shaped cells, which are frequently obliterated. 

Xylem. The xylem contains vessels, wood parenchyma, 
and medullary rays. 

The vessels are large, rounded cells with thick walls. 



ROOTS AND RHIZOMES 



227 



The wood parenchyma consists of thick- walled cells of irreg- 
ular size and form. 

The medullary rays are tangentially elongated and rectangular 
in form. 

Pith parenchyma. The pith parenchyma cells are rounded 
in outline and as large as the cortical parenchyma cells. 

POWDERED PINK ROOT 

When the roots and rhizomes of spigelia are powdered (Plate 
93) they show the following structure: 

The epidermal cells are small and brownish on surface view, 
varying in size from 13 by 18 micromillimeters to 31 by 40 
micromillimeters. When associated with parenchyma they ap- 
pear as black masses. The cortical parenchyma cells are rounded 
and vary in size from 23 by 26 micromillimeters to 37.5 by 90 
micromillimeters. Many of the cells from the root contain 
larger quantities of minute single rounded starch grains varying 
in size from 1 micromillimeter to 4 micromillimeters. The 
larger round single starch grains are found in both the cortical 
and pith parenchyma of the rhizome. They vary in size from 
5 micromillimeters to 18 micromillimeters. The conducting 
elements are pitted tracheids varying from 10 micromillimeters 
to 38 micromillimeters in diameter. A few pitted and annular 
vessels are also found. The only fibres occurring are found in 
the xylem. They are not a prominent feature of the powder, 
as their walls break up into minute fragments. The pith 
parenchyma varies in size from 13 by 19 micromillimeters to 
75 by 82.5 micromillimeters. It is in these cells that the largest 
starch grains occur. 

Distinguishing diagnostic characters of the powder: 

1. Parenchyma with starch. 

2. Dark masses of epidermal tissue. 

3. Spigelia should contain starch, and it should not contain 
cystoliths, stone cells, or long, white- walled bast fibres. 

POWDERED RUELLIA ROOT 

When the roots of ruellia root and rhizome are powdered 
(Plate 94) they show the following structure: 

The epidermal cells vary from 7.8 by 15.6 micromillimeters 



PLATE 93 




Powdered Spigelia marylandica, L. 

I. Epidermis and cortical parenchyma. 2. Tracheids and fibres. 3. Par- 
enchyma cells of the root containing the small starch grains, longitudinal view. 
4. Parenchyma of the rhizome containing the large starch grains, transverse 
view. 5. Tracheids. 6. Surface view of the epidermal cells. 7. Starch scattered 
through the field. 8 and 8'. Dark masses of epidermal and underlying tissue. 



PLATE 94 




Powdered Ruellia ciliosa, Pursh. 



i. Short, broad cystoliths from the rhizome, i'. Long cystoliths from the 
root. 2 and 2'. Long, narrow, white-walled bast fibres. 3. Tracheal tissue 
from the xylem of the stem. 4. Root parenchyma. 5. Tracheal tissue from 
the xylem of the root. 6. Cortical parenchyma cells from the rhizome with 
short, broad cystoliths. 7 and 7'. Long, thick-walled sclerids from the root. 
8. Short, broad sclerids from the stem. 9. Pitted pith parenchyma from the 
stem with intercellular space. 10. Parenchyma of the root with sclerid and 
cystolith, longitudinal view. 



230 



HISTOLOGY OF MEDICINAL PLANTS 



to 1 5. i by 16.6 micromillimeters. The cell contents are dark 
and the walls are light. A few rows of the outer cortical paren- 
chyma cells of both the rhizome and the root have dark cell 
contents and white walls. The dark contents disappear toward 
the phloem. The cortical cells vary from 13.6 by 14.3 micro- 
millimeters to 89.5 by 90.9 micromillimeters. In the cortical 
parenchyma cells of the rhizome are found the short, broad 
cystoliths measuring up to 52 by 62 micromillimeters. In the 
corresponding cells of the root are found the long, narrow cysto- 
liths which measure up to 68.4 by 187.2 micromillimeters. 
Scattered throughout the powder are seen three distinct types 
of sclerids (stone cells) which are associated with the cortical 
parenchyma of both the stem and the root. Most of them are 
found, however, in the roots. First, the short, broad stone 
cells from the stem basis have square ends; the walls vary from 
13 to 19.5 micromillimeters in thickness with branching pores 
which extend toward the adjacent cell. These sclerids vary in 
size from 52 by 54.6 micromillimeters to 45 by 130 micromilli- 
meters. Secondly, the long stone cells from the root vary from 
32 by 96 micromilhmeters to 45.5 by 542.5 micromilhmeters 
with walls 16 micromillimeters thick. The width of the cell 
and the thickness of the wall vary but little throughout their 
entire length. The third type of stone cell also from the root 
has unequally thickened walls and the ends are square or blunt. 
A few long, narrow, colorless, thin-walled bast fibres also occur. 
They are 13 micromilhmeters wide, with walls 3.9 micromilli- 
meters thick. Annular spiral and pitted vessels are also found 
scattered throughout the powder. 

The diagnostic characters of the powder are: 

1. The short, broad, and long, narrow cystoliths. 

2. The short, broad, and long, narrow sclerids. 

3. The long, narrow, thin, white-walled bast fibres. 

In poke root, ipecac, sarsaparilla, and veratrum are raphides. 
In belladonna and horse- nettle roots are micro-crystals. In 
calumba, stillingea, krameria, licorice, scamony root are prisms. 
In saponaria, jalap, althea, spikenard, rumex, rhubarb are 
rosette crystals. In pleurisy roots both prisms and rosettes 
occur. 

In gentian, senega, symphytuns, lovage, parsley, inula, 



ROOTS AND RHIZOMES 



231 



echinacea, angelica, burdock, and chicory no crystals of any 
kind occur. Root hairs occur in cross-sections of sarsaparilla 
root and false unicorn, but with these exceptions : root hairs do 
not occur on roots, because the younger part of the root with 
root hairs is not removed from the soil when the drug is collected. 
In sarsaparilla root there are several layers of hypodermal cells; 
in most roots there are no hypodermal cells. In the non- woody 
roots or the roots of herbs the parenchyma cells form the greater 
part of the tissues of the root. In ruellia root are stone cells; 
in spigelia root and many other roots there are no stone cells. 
In ruellia root are bast fibres; in spigelia, gentian, ipecac, chicory, 
dandelion, Symphytum, and lovage no bast fibres occur. In 
all the woody roots there is a periderm consisting of typical 
cork cells, as in black haw; or stone cells, as in asclepias; or 
of a mixture of lifeless parenclryma, medullary rays, etc., as in 
Oregon grape root. 

Woody roots have a phellogen layer which is absent in the 
non-woody roots. 

The numbers of layers of cortical parenchyma differ in the 
same root according to its age, but for a given root there is a 
normal variation. 

The number of layers of cortical parenchyma in proportion 
to other cells is less in woody roots. 

In woody roots there is no endodermis. The cambium in these 
cases shows clearly between the phloem and the xylem part of 
the fibro-vascular bundle. 

In woody roots the wood fibres are well developed and form 
a large part of the root, and the medullary rays have pitted 
side and end walls. 

The description given above of ruellia root is not typical of 
all roots, but the structure represents the greater number of 
the elements that it is possible to find in a root. In many roots, 
for instance, there are no stone cells, in others no epidermis 
and no endodermis. In asclepias, aconite, and calumba stone 
cells occur. In Symphytum, chicory, dandelion, burdock, elecam- 
pane, pyrethrum, gentian, and senega no stone cells occur. In 
aconite, althea, asclepias, belladonna, bryonia, columba, ipecac, 
jalap, krameria, sarsaparilla, scamony, stillingea, and rumex 
are characteristic starch grains. Symphytum, chicory, dande- 



232 



HISTOLOGY OF MEDICINAL PLANTS 



lion, burdock, elecampane, and pyre thrum contain inulin, but 
no starch. In saponaria, gentian, and senega neither starch 
nor inulin occurs. 

When studying roots the nature of the epidermis or the 
periderm must be considered, as also the number of layers of 
cortical parenchyma; the occurrence, distribution, and amount 
of stone cells when present; the presence or absence of the 
endodermis; the occurrence and structure of bast fibres when 
present; the nature of the cambium cells; the width and struc- 
ture of the medullary rays, the size of the wood fibres and wood 
parenchyma, and the nature of the cell contents and the ar- 
rangement of the fibro-vascular bundle. 



CHAPTER II 



STEMS 

When studying stems it should first be determined whether 
they were derived from monocotyledonous or dicotyledonous 
plants. This fact is ascertained by determining the type of 
the fibro-vascular bundle. See Chapter XL The next fact 
to determine is whether the stem is from an herb or from a woody 
plant. This fact is readily determined because herbaceous 
stems have a true epidermis, masses of collenchyma at the 
angles of the stem. The cortical cells contain chlorophyll, and 
the pith is very large. Woody stems have a corky layer, a 
phellogen layer, and the pith is very small except in the very 
young woody stems. 

Having determined these facts, a study should be made of 
the arrangement, form, structure, color, and the cell contents 
of the different cells in order to determine the species of plant 
from which the stem was obtained. 

HERBACEOUS STEMS 

The great variation in the structure of herbaceous stems is 
shown in the cross-sections of spigelia (Plate 95); in ruellia 
(Plate 96); in the charts of powdered genuine horehound, 
powdered spurious horehound, and in the chart of powdered 
insect flower stems. 

CROSS-SECTION SPIGELIA STEM 

Spigelia stem (Plate 95) has the following characteristic 
structure : 

Epidermis. The epidermal cells are papillate. 

Cortex, The cortical parenchyma cells consist of tan- 
gentially elongated cells which are oval in outline. 

Phloem. The phloem consists of sieve cells, phloem paren- 
chyma, and of bast fibres. 

233 



PLATE 95 





Cross-Section of Stem of Spigelia marylandica, L. 
. Papillate epidermis. 4- Phloem. 7- Inner phloem. 

. Cortical parenchyma. 5- Cambium. 

. Bast stereome. 6. Xylem. 



STEMS 



235 



The sieve cells are small, and with thin, white, angled 
walls. 

The phloem parenchyma resembles the sieve cells, but they 
are larger. 

The bast fibres are rounded in outline and the walls are 
thick, white, non-porous, and non-striated. 

Cambium. The cambium cells are rectangular in shape or 
the walls are collapsed and the cells indistinct. 

Xylem. The xylem contains vessels, wood parenchyma, 
medullary rays. The vessels are small and angled, the walls 
are thick and white. 

Wood parenchyma. The cells are variable in size and shape, 
and the walls are thick. The medullary ray cells are small, 
narrow, and tangentially elongated. 

Internal Phloem. External to the pith parenchyma are 
isolated groups of internal phloem consisting of sieve cells. 

Pith Parenchyma. The pith parenchyma cells are oval in 
form and irregularly placed. The cells contain small, simple 
starch grains. 

RUELLIA STEM 

The cross-section of ruellia stem (Plate 96) is as follows: 

Epidermis. The epidermal cells are variable in shape and 
very large. There are no cell contents. 

Cortex. The cortex consists of collenchyma and parenchyma 
cells and stone cells. 

The collenchyma cells have very small, angled cavities and 
very thick walls. These cells make up the greater part of the 
cortex. 

The cortical parenchyma cells are variable in size and shape. 
The stone cells occur singly or in groups. The walls are thick, 
white, porous, and striated, and the central cavity is frequently 
quite large. 

Phloem. The phloem contains sieve cells, phloem paren- 
chyma, and bast fibres. 

The sieve cells have thin, white, angled walls. 

The phloem parenchyma cells are frequently tangentially 
elongated, otherwise they resemble the sieve cells. 

The bast fibres occur alone or in groups. The walls are 
thick, white and porous. 



PLATE 96 




Cross-Section of Stem of Ruellia ciliosa, Pursh. 

I. Epidermis. 2. Collenchyma. 3. Parenchyma. 4. Sclerids. 5. Bast 
fibres. 6. Phloem. 7. Cambium cells. 8. Xylem. 10. Pith parenchyma. 



STEMS 



237 



Cambium. The cambium cells are rectangular in shape 
and the walls are thin. 

Xylem. The xylem contains vessels, wood parenchyma, and 
medullary rays. 

The vessels are large; the walls are thick, white, and angled. 

The wood parenchyma cells are variable in size and shape 
and the walls are angled. 

The medullary ray cells are radially elongated and rectangu- 
lar in shape. 

Pith Parenchyma. The pith parenchyma cells are large and 
rounded in shape. 

POWDERED HOREHOUND 

The structure of powdered horehound is shown in Chart 97. 
The epidermal cells of the leaf (1) are wavy in outline, the guard 
cells are elliptical, the stoma lens-shaped, the epidermis often 
showing hairy outgrowth as in the illustration. The epidermal 
cells of the petals (2) have irregularly thickened beaded walls. 
The non-glandular hairs from the calyx (3); the long, thin- 
walled, multicellular non-glandular twisted hairs (4) from the 
leaves and stems; long, thin-walled, unicellular hairs (5) from 
the tube of the corolla; the glandular hairs (6) with a one-celled 
stalk and with two secreting cells divided by vertical walls; the 
eight-celled glandular hair (7) as seen in surface and side view; 
the spiral and reticulated conducting cells (8) ; the thick, white- 
walled fibres from the stem (9); the pollen grains (10) with 
nearly smooth walls. 

The diagnostic elements of the U. S. P. horehound are the 
long, twisted, multicellular hairs (4), the glandular hairs (7), 
and the pollen grains (10). 

POWDERED SPURIOUS HOREHOUND 

Marrubium perigrinum, which is a related species of hore- 
hound and which is a common adulterant of horehound, has 
the following structure (Plate 98) : 

The wavy leaf epidermis (1) with stoma; the beaded wall 
petal epidermis (2); the non-glandular, multicellular branched 
hairs (3) from the stem leaves or flowers; the broken pieces and 
branches of the compound hairs (4) scattered throughout the 



PLATE 97 




Powdered Horehound {Marrubium vulgare, L). 

I. Epidermis of leaf showing the wavy epidermal cells, stoma, and a 
clustered hair. 2. Surface view of the petal epidermis. 3. Non-glandular 
hair from the calyx or corolla. 4. Long, thin-walled, twisted, non-glandular 
hairs from the leaves and stem. 5. Unicellular non-glandular hair from the 
tube of the corolla. 6. Glandular hairs with a one-celled stalk and with two 
secreting cells divided by vertical walls. 7. Surface and side view of the 
eight-celled glandular hairs. 8. Conducting cells. 9. Fibres from the stem. 
jo. Pollen grains. 




Spurious Horehound (Marrvbium peregrinum, L.) 



I. Surface view of the leaf epidermis. 2. View of the petal epidermis. 
.3. Non-glandular multicellular branched hair from the stem, leaves, or flowers 
with a few of the lower branches broken. 4. Broken pieces and branches from 
the compound hairs scattered throughout the field. 5. Unicellular glandular 
hair with a two-celled stalk. 6. Under-surface view of an eight-celled gland- 
ular hair. 7. Side view of eight-celled glandular hair. 8. Long, pointed, 
unicellular, non-glandular hair from the corolla, the wall irregularly thickened 
near the apex. 9. Fibres. 10. Pollen grains. 11. Conducting cells of leaf. 



PLATE 99 




Powdered Insect Flower Stems {Chrysanthemum cineraru 'folium, 
[Trev.], Vis.) 

. Surface view of epidermis. 5. Cross-section of fibres. 

. Cross-section of epidermis. 6. Longitudinal view of pith parenchyma. 
. Hairs. 7. Cross-section of pith parenchyma. 

. Fibres . 8. Conducting cells. 



STEMS 



241 



field; the glandular hairs (5) with a two-celled stalk; the eight- 
celled glandular hair (7) seen in surface view and a side view (8) 
of a similar hair; the long, pointed, unicellular non-glandular 
hair from the tube of the corolla, the wall irregularly thickened 
near the apex; the fibres (9) from the stem; the pollen grains 
(10) with prominent centrifugal projections; the conducting 
cells. 

The diagnostic elements of marrubium perigrinum are the 
multicellular branched hairs (3) which occur on all parts of the 
plant, usually much broken in the powder, with walls many 
times thicker than the walls of the hairs found in U. S. P. hore- 
hound; the pollen grains (10) with centrifugal projections and 
the stalked glandular hairs (5). 

INSECT FLOWER STEMS 

Insect flower stems are the chief adulterant of insect flowers. 
Until the passage of the insecticide law, it was a common practice 
to sell (for insect powder) a mixture of powdered stems and 
flowers. Since the passage of the law, the presence of the stems 
in a powder is supposed to be declared on the label. In spite 
of the penalties attached, their presence in a powder is frequently 
not declared, as evidenced by a microscopical examination of 
the insect powders obtained in the open market. 

The structure of powdered insect flower stems (Chart 99) is 
as follows: 

The epidermal cells of the stems are prominently marked 
with stoma and angled, striated wall cells (Fig. 1). On cross- 
section (Fig. 2) the stem is seen to be made up of epidermal 
cells with thick outer and thin side walls (Fig. 2) . The T-shaped 
hairs (Fig. 3) are longer than those found on any other part of 
the plant. The fibres (Fig. 4) are the most characteristic part 
of the powder. They are elongated, and the walls are white 
and slightly porous and of nearly uniform thickness. They 
occur free in the field or in groups of two or more. The 
cross-section view of these fibres is shown in Fig. 5. The pith 
parenchyma (Fig. 6) is abundant and is composed of thick, 
porous- walled cells. On cross-section the cells are rounded 
and are separated by intercellular spaces. The conducting cells 
(Fig. 8) vary from spiral to reticulate. 



CHAPTER III 



WOODY STEMS 

BUCHU STEM 

The cross-section of a biichu stem (Plate C) 1.6 millimeters 
in diameter, showing a few of the epidermal cells modified into 
thick- walled, roughish, unicellular trichomes (1). The remain- 
ing epidermal cells have a thick, wavy outer wall (2). Beneath 
the epidermis are several rows of cortical parenchyma cells (3) 
which extend to the bast bundles and in which are found the 
secretory cavities with the thin-walled secretory cells (4). The 
bast fibres (5) occur in continuous bands, varying greatly in size; 
the walls are whitish and of variable thickness. Inside the 
bast fibres, the small irregular sieve cells (6) occur in groups, 
surrounded by the phloem parenchyma (8). The radially 
elongated cells of the medullary rays (7) extend outward from 
the xylem, increasing in number in the outer portions of the 
wood, and extending nearly to the bast fibres. No distinct 
cambium layer is visible. The conducting cells (9) occur 
throughout the xylem surrounded by the wood fibres and wood 
parenchyma (10). The latter is not very abundant in buchu. 
The medullary rays border on the conducting cells and extend 
outward to the phloem. The pith parenchyma cells are nearly 
circular in outline and often show a perforated end wall when 
a cell happens to be cut just above or below that point. 

MATURE BUCHU STEM 

In Plate 101-A is shown the cork formation or secondary 
growth as seen in the older, larger buchu stems. The wavy 
epidermis (1), which is the primary epidermis and which has 
disappeared on many portions of the stem, has thin side walls 
and dark cell contents (2). Next to the epidermal cells occur 
several rows of peculiarly arched cork cells with thick, white 
outer walls (3} and reddish-brown cell contents (4). The cork 

242 



PLATE ioo 




Cross-Section of Buchu Stems (Barosma betulina [Berg.], Barth. andWendl.) 

I. Hairs. 2. Wavy epidermis. 3. Cortical parenchyma. 4. Secretion 
cells and cavity. 5. Group of bast fibres. 6. Sieve cells. 7. Medullary rays. 
8. Phloem parenchyma. 9. Vessels. 10. Wood fibres, and wood parenchyma. 
11. Pith parenchyma. 



PLATE 101 




A. Cross-section of buchu stem (Barosma betulina [Berg.], Barth. and 
Wendl.). I, Outer wall of epidermis; 2, Cell cavity of epidermal cell; 3, Wall 
of cork cell; 4, Cavity of cork cell; 5, Phellogen layer; 6, Divided phellogen 
cell changing into a cortical parenchyma cell; 7, Cortical parenchyma cell. 

B. Cross-section of leptandra rhizome {Leptandra virginica [L.], Nutt.). 
I, Parenchyma cells undergoing change in the composition of their walls; 2, A 
break in the epidermal tissue; 3, Parenchyma cells undergoing division. 



WOODY STEMS 



245 



cambium (5) is typical in form, and it has formed one or two 
layers of phelloderm cells (6) which have the same form as the 
cambium cells but with thicker walls. Next to the phelloderm 
occur the cortical parenchyma cells. The remaining structure 
of the mature stem is identical with that of Fig. 2. 

POWDERED BUCHU STEM 

Powdered buchu stem (Plate 102) has many striking features 
which make it easy of identification when mixed with buchu 
leaves. A few unicellular, rough, thick, white-walled trichomes 
(1) occur distributed throughout the field. They are straight 
or shghtly curved and vary in length from 40 to 100 microns; 
in thickness at the bast they measure from 10 to 22 microns. 
The central cavity varies greatly, and in some trichomes seems 
to have disappeared entirely. The epidermal cells (2) are very 
characteristic, occurring singly or in groups of two or more. 
The cells from the older stems often appear reddish brown by 
transmitted light, while the epidermal cells from the younger 
stems appear whitish opaque (porcelain-like) . They are usually 
six-sided and angular in outline. The cortical parenchyma 
cells (3) on transverse view have a rounded cell cavity and 
intercellular spaces between the walls. The double walls vary 
in thickness, the greatest thickness being about 9 microns. The 
parenchyma cells (3) on longitudinal view show square ends 
and often contain sphaero-crystalline masses of hesperidin. The 
thin-walled sieve cells and the surrounding cells are scarcely 
ever seen in the powder. The white- walled pointed stereomes 
(4) are a characteristic feature of the powder ; they vary greatly 
in length, in diameter and in the thickness of their walls. In 
a number eighty powder the fibres are mostly broken. The 
greatest length of the unbroken fibres is 1.25 microns. The 
thickest wall measured 5 microns and the greatest observed 
width was 25 microns. The spiral reticulate and scalariform 
thickened conducting cells occur scattered throughout the 
powder. The reticulate and scalariform cells usually occur with 
wood fibres. It is an interesting fact that the spiral thickening 
in conducting cells is usually separate from the side wall and 
nearly always appears as indicated at 5. An occasional rosette 
crystal of calcium oxalate (6) is seen in the field. The wood 



PLATE 102 




Powdered Buchu Stems (Barosma betulina (Berg.], Barth. and Wendl.). 
I. Hairs. 2. Epidermal cells, the larger pieces reddish-brown; the smaller 
aggregations white. 3. Transverse cortical parenchyma, 3'. Longitudinal 
cortical parenchyma with sphsero crystalline masses of hesperidin. 4. Bast 
fibres. 5. Spiral, sclariform, and reticulate vessels. 6. Rosette crystals of 
calcium oxalate. 7. Wood parenchyma. 8. Pith parenchyma with porous 
side and end walls. 9. Wood fibres. 



WOODY STEMS 



247 



parenchyma (7), which makes up a very small percentage of 
the xylem, is not readily found in the powder. The pith paren- 
chyma cells (8) have thick, porous side walls and perforated side 
walls. The wood fibres (9) usually occur in masses surrounding 
the conducting cells; when occurring singly, the oblique pores 
readily distinguish them from the bast fibres. 

The diagnostic elements of powdered buchu stems are: 
First, trichomes; secondly, reddish-brown and white-angled 
epidermal cells; thirdly, the long, white bast fibres. 



CHAPTER IV 



BARKS 

Barks are all obtained from dicotyledonous plants. In 
studying barks there should be ascertained the thickness, ar- 
rangement, form, structure, color, and cell contents of the cells 
occurring in the outer, middle, and inner barks. 

The outer bark includes the cork cells and the phellogen 
layer. The middle bark includes all the cells occurring between 
the phellogen layer and the beginning of the medullary rays. 
The inner bark includes the medullary ray cells and all cells 
associated with them. The plan of structure of all barks is 
similar, .but in each species of plant the structure of the bark 
is uniform and characteristic for the species. 

A great number of drugs consist of the bark of woody plants ; 
for this reason the bark is considered in a separate chapter from 
the stem. 

WHITE PINE BARK 

The cross-section of white pine bark (Plate 103) has the 
following structure: 

Outer Bark, The periderm consists of several layers of 
reddish-brown cork cells (1) which are narrow, elongated, and 
with thin walls. 

Middle Bark. The cells forming the middle bark are paren- 
chyma and secretion cells. 

The parenchyma cells vary greatly in size, form, and thick- 
ness of the walls. The cells beneath the cork cells and around 
the secretion cells are tangentially elongated and oval in shape, 
while the other parenchyma cells are more irregular in shape. 

The secretion cells are arranged around the schizogenous 
secretion cavities. The cells are tangentially elongated, and the 
walls, which are slightly papillate, are white. 

Inner Bark. The cells forming the inner bark are medullary 
rays, parenchyma, sieve cells, and storage cavities. 

248 



PLATE 103 




Cross-Section of Unrossed White Pine Bark {Pinus strobus, L.) 

1. Cork cells of the epidermis. 2. Parenchyma cells filled with chlorophyl. 
3. Intercellular space. 4. Secretion cavity with resin. 5. Secretion cells. 
6. One or more circles of parenchyma filled with chlorophyl. 7. Parenchyma. 
8. Medullary rays. 9. Sieve cells. 10. Storage cavities. 




250 



HISTOLOGY OF MEDICINAL PLANTS 



The medullary rays form wavy lines. The medullary ray 
cells are radially elongated, rectangular in shape, and they con- 
tain granular cell contents. The sieve cells are either square 
or rectangular in shape. The walls are thin and white. The 
storage cavities are either rilled with starch or with prisms 
and tannin. 

POWDERED WHITE PINE BARK 

White pine bark (Plate 104) when powdered shows the 
following characteristic elements: 

The microscopic structure of a powdered white pine is as 
follows: The epidermis (1) consists of reddish-brown masses, 
irregular in outline. The outer parenchyma cells are of a bright- 
green color, owing to the presence of chlorophyll. (The above 
elements are not usually found in the rossed bark.) The paren- 
chyma (3) with starch usually occurs in longitudinal sections 
accompanied with sieve cells. Often the tissue separates trans- 
versely, showing the medullary rays (4) with their granular cell 
contents (9) and the inner parenchyma cells rilled with starch 
and the surrounding sieve cells. 

The crystals are nearly perfect cubes and occur singly (5) 
or in groups (6). On the longitudinal section of the bark the 
crystals occur in parenchyma cells surrounded by a reddish cell 
content and form parallel rows which are very characteristic. 
The resin occurs either as white, angled fragments (7) in a water 
mount, or as globular mass (8) or as reddish-brown pieces (10). 
The starch is very abundant and is distributed through the 
field. The diagnostic grain is lens-shaped, with a cleft hilum, 
which is nearly straight, or slightly curved, and runs parallel 
to the long diameter of the grain. The addition of ferric 
chlorid T. S. will show the presence of tannin by forming a 
dark coloration. The identification of the starch is facilitated 
by the addition of a weak Lugol's solution, which imparts a 
blue coloration to the starch grain. 

The form, amount, and distribution of the cells composing 
the bark differ greatly in different plants. 

In cramp bark the cork and phellogen cells are very large, 
while in cascara sagrada the phellogen and the cork cells are 
very small. 



PLATE 104 




Powdered White Pine Bark {Pinus strobus, L.) 

1. Epidermis. 2. Parenchyma cells. 3. Parenchyma with starch. 4. 
Medullary rays. 5. Solitary crystals. 6. Solitary crystals and tannin. 7, 8 
and 10. Resin masses. 9. Starch. 



252 



HISTOLOGY OF MEDICINAL PLANTS 



In canella alba bark the periderm is composed of stone- 
cell cork or stone cells arranged in superimposed rows, which 
form the outer layers of the bark. 

In white oak and most barks from woody trees the periderm 
consists of lifeless parenchyma, medullary rays, sieve cells, 
bast fibres, and in some cases stone cells and of phellogen 
cells. 

In young wild cherry, cascara sagrada, and frangula are 
several layers of tangentially elongated collenchyma cells with 
chlorophyll. In the older barks of the above and in many 
other barks no collenchyma cells occur. 

In cramp bark and in tulip tree bark the outer layers of the 
cortical parenchyma cells are beaded. In most barks there is 
no beaded walled parenchyma. The outer layers of most 
cortical parenchyma cells are tangentially elongated while the 
inner parenchyma cells are mostly circular in outline. 

In white oak, cascara sagrada and prickly ash are groups 
of stone cells; in the cinnamon barks are "bands of stone cells; 
in cinchona bark are isolated stone cells. In cramp bark, 
mezerum, elm, and white pine bark no stone cells occur. 

In frangula, cascara sagrada, cocillina, cinnamon, cinchona,, 
sassafras, and wild cherry barks the bast fibres occur in groups. 
In frangula, cascara sagrada, and cocillina the bast fibres are 
surrounded by crystal cells with crystals. 

In sassafras bark mucilage cells occur. In canella alba, 
white pine, and sassafras barks secretion cells occur; but in 
most barks no secretion cells occur. 

In sassafras bark the medullary ray cells are nearly as broad 
as long; in cramp bark they are elongated and oval in shape. 
In cascara sagrada, as in most barks, the cells are longer than 
broad and rectangular in shape. 

In cascara sagrada the sieve cells are very large ; in granatum 
bark the sieve cells are very small. 

In cassia cinnamon and in canella alba bark the walls of the 
sieve cells have collapsed, with the result that the sieve cells 
have become partly obliterated. 

In witch-hazel, mountain maple, willow, and black walnut 
are found prisms; in cramp bark, black haw, wahoo, pome- 
granate, and cotton root bark are found rosette crystals; in 



BARKS 



253 



the cinnamon barks are found raphides; in cinchona bark, 
micro-crystals. 

In cocillina, frangula, cascara sagrada, white oak, poplar 
and Jamaica dogwood barks are found crystal-bearing fibres 
(Plates 19 and 20). 

When studying barks we must consider the kind, structure, 
and amount of the periderm; the nature of the phellogen; the 
nature and amount of the cortical parenchyma; the occurrence, 
distribution, and amount of stone cells, when present; the 
occurrence and structure of the bast fibres; the presence or 
absence of secretion cells; the width, distribution, and structure 
of the medullary rays. 



CHAPTER V 



WOODS 

Quite a number of drugs consist of the wood of woody plants; 
such drugs are quassia, red saunders, white sandalwood, and 
guaiac. 

When studying woods it is necessary to observe the cross, 
tangential, and radial sections. Such sections of quassia are 
shown in Plates 105, 106, and 107. When studying these sec- 
tions it should be remembered that while the types of cells form- 
ing quassia wood are similar to the cells forming other woods, 
still their structure, arrangement, and amount will vary in a 
recognizable way in the different woods. 

CROSS-SECTION QUASSIA 

Plate 105 is a cross-section of quassia. It has the following 
structure : 

Vessels. The vessels occur singly or in groups of two to 
eight cells. The cells are variable in size and shape. The 
walls are yellowish white and porous. 

Medullary Rays. The medullary rays vary from one to five 
cells in width. 

The medullary ray cells are radially elongated and the walls 
are strongly porous. 

Wood Parenchyma. The wood parenchyma cells have thin, 
yellowish- white, angled walls. 

Wood Fibres. The wood fibres have thick, yellowish- white, 
angled walls. These cells are smaller in diameter than the 
wood parenchyma cells. 

RADIAL SECTION QUASSIA 

The radial section of quassia (Plate 107) is as follows: 
Vessels. The vessels appear as in the tangential section. 
Medullary rays. The medullary rays vary from ten to 

254 



PLATE 105 




Cross-Section of Quassia Wood (Pier ana excelsa [Sw.], Lindl.) • 

1. Vessels. 

2. Medullary rays. 

3. Wood parenchyma. 

4. Wood fibres. 



PLATE 1 06 




PLATE 107 




Radial Section of Quassia Wood (Pier ana excelsa [Sw.], Lindl.) 

1. Showing the height and length of the medullary rays and cells. 

2. Cells with starch. 

3. Wood parenchyma and wood fibres. 



258 



HISTOLOGY OF MEDICINAL PLANTS 



twenty cells in height according to the part of the medullary 
ray bundle cut across. 

The medullary ray cells exhibit their height and length. 
The walls of the cells are yellowish white and strongly 
porous. 

Wood Parenchyma. The wood parenchyma cells have 
yellowish, thin walls and blunt end walls. 

Wood Fibres. The wood fibres have thick, yellowish- white 
walls, and the end of the cells are strongly tapering. 

TANGENTIAL SECTION QUASSIA 

The tangential section of quassia (Plate 106) shows the 
following structure: 

Vessels. The vessels are very long and broad and the 
yellow walls are marked with clearly defined pits. 

Medullary Rays. The tangential section shows the cross- 
section of the medullary ray bundle and the cross-section of 
the medullary ray cell. 

The medullary ray bundle varies in width from one to five 
cells. The ends of the bundles are always one cell in width, 
while the central part of the bundle is frequently five cells 
in width. 

The medullary ray cell varies in size, structure, and shape 
according to the part of the cell cut across. The cells cut 
across the centre show hollow spaces, but the cells cut just 
above or below the end wall show a strongly pitted surface. 
The cells forming the end of the bundle are larger than the cells 
forming the centre of the bundle. 

Wood Parenchyma. The wood parenchyma cells are greatly 
elongated and the walls are thin and yellowish white. The 
ends of the cells are blunt. 

Wood Fibres. The wood fibres are elongated, the walls 
are thick and the cells are strongly tapering. 

In quassia, white sandalwood, red sandalwood, and guaiac 
wood are characteristic crystals. 

In quassia the vessels are finely pitted, yellowish, and dis- 
tinct ; in white sandalwood the vessels are coarsely and sparingly 
pitted and white translucent; in red saunders the vessels are 
coarsely pitted, bright red and distinct. 



WOODS 



259 



When studying woods we must consider the width of the 
medullary rays, the structure and cell contents of the medullary 
ray cells; the structure, color, and cell contents of the wood 
parenchyma; also the wood fibres. 



CHAPTER VI 



LEAVES 

Leaves collectively constitute the greatest manufacturing 
plant in the world. Most of the food, clothing, and medicine 
used by man is formed as a result of the work of the leaf. The 
cell contents, structure, and arrangement of the different cells 
of the leaf differ in a marked degree from the cell contents, 
structure, and arrangement of the cells in the other organs of 
the plant. This accounts for the presence of the large amount 
of chlorophyll in the leaf, the presence of stomata, and the 
peculiar arrangement of the cells. 

It should be ascertained if the stomata are above, even with, 
or below the epidermis; the nature of the epidermal cells, and, 
when present, the nature^ of the hypodermal cells; the number of 
layers of palisade parenchyma and whether it is present on 
both surfaces of the leaf, and the nature of the outgrowths from 
the epidermal cells. 

KLIP BUCHTJ 

The cross-section of klip buchu (Plate 108) has the following 
structure : 

Epidermis. The epidermal cells of klip buchu are modified 
to form papillae, the walls are yellowish white, and the papillate 
portion of the cell is nearly solid. 

Hypodermis, The hypodermal cells are never intact because 
the mucilage contained in the cells swells when placed in water 
and breaks the thin side walls. 

Upper Palisade Parenchyma. The palisade parenchyma is 
two layers in thickness. The cells of the outer layer are greatly 
elongated and are packed with chlorophyll. The inner layer 
of palisade cells is more irregular, and the cells are much shorter 
than the cells of the outer palisade layer. 

Spongy Parenchyma. The spongy parenchyma cells are 

260 



PLATE 1 08 




DDQP 




Cross-Section of Klip Buchu just over the Vein 

A. Papillate upper epidermis. 

B. Hypodermal cells with broken side walls, due to expansion of mucilage 
contents. 

C. Palisade cells, showing two cells filled with chlorophyll. 

D. Palisade like mesophyll. 

E. Endodermis. 

F. Vascular strand of vein. 

G. Conducting cells with spirally thickened walls. 

H. Characteristic leaf mesophyll. 

/. Short, thick palisade cells on the under side of leaf, just under the vein. 
/. Under hypodermal cells. 
K. Papillate under epidermis. 



262 



HISTOLOGY OF MEDICINAL PLANTS 



branched; therefore, large intercellular spaces occur between 
the cells. 

Under Palisade Parenchyma. The palisade cells of the 
under epidermis are short and broad, and they contain fewer 
chlorophyll grains than the upper palisade cells of the upper 
epidermis. These cells occur only under the veins. 

Under Hypodermis. The under hypodermal cells are shorter 
and broader than the upper hypodermal cells. 

Under Epidermis. The under epidermal cells are modified 
to form papillae which are similar to the papillae of the upper 
epidermis. 

Fibro-Vascular Bundle. The cells composing the vascular 
bundle are sieve cells, vessels, and fibres. 

The sieve cells are small and the walls are white and 
angled. 

The vessels have thick, white, angled walls. 
The bast fibres are rounded in outline and the walls are thick 
and white. 

Endodermis. The endodermal cells encircle the fibro-vascu- 
lar bundles. The cells are large, thin- walled, and oval in shape. 

Secretion Cells. Near the edges of the leaf are schizoge- 
nous secretion cavities surrounded by thin- walled secretion 
cells. 

POWDERED KLIP BTJCHU 

When the leaf is powdered (Plate 109), the cells are quite 
as characteristic in appearance. The upper epidermal cells 
(1) have thick-beaded, yellowish- white walls and papillate outer 
walls. No stomata occur on the upper surface. The under 
epidermis (2) with numerous stomata, is surrounded by the 
characteristic guard cells. The end walls are beaded as on the 
upper surface. The palisade cells (3) appear as in the cross- 
section. The conducting cells (4 and 4) are of the spiral and 
pitted type. The papillae (5 and 5) are very abundant in the 
powder and very characteristic. The fragments of the epidermis 
(6) are also abundant. The mesophyll (7) is characteristic, as 
it retains its form when powdered. The fibres (8) are usually 
associated with the conducting cells; occasionally they are 
found free as in the illustration. 



PLATE 109 




Powdered Klip Buchu 

I. Upper epidermis. 2. Under epidermis. 3. Palisade cells with chloro- 
phyll 4 and 4. Conducting cells. 5 and 5. Papillae. 6. Fragments of the 
epidermis. 7. Mesophyll. 8. Fibres. 



264 



HISTOLOGY OF MEDICINAL PLANTS 



MOUNTAIN LAUREL 

Epidermis. The epidermal cells of mountain laurel are oc- 
casionally modified, as unicellular hairs (Plate no, Fig. i), 
particularly in the region of the veins. The ordinary epidermal 
cells have thick outer walls and thin inner walls. Beneath 
many of the epidermal cells are large air-spaces. 

Upper Palisade Parenchyma. The palisade parenchyma 
vary from four to five layers. The inner palisade cells are 
shorter and broader than the outer layer of cells. 

Parenchyma. The parenchyma cells (Fig. 4) are rounded 
in form and they are arranged in the form of columns which are 
one cell in thickness above, but two to three cells in thickness 
near the under epidermis. Between each chain of cells is a 
larger intercellular space (Fig. 6) . In a few of the cells are large 
rosette crystals. 

Under Epidermis. The under epidermal cells are uniformly 
smaller than the upper epidermal cells. 

It is thus seen that mountain laurel leaf has no hypodermal 
cells; no spongy parenchymal no under palisade cells; no under 
hypodermal cells, and no secretion cavities. 

TRAILING ARBUTUS 

Epidermis. The epidermal cells of the trailing arbutus 
(Plate in, Fig. 2) are variable in size. Many of the cells are 
modified, as guard cells (Fig. 1). 

Parenchyma. The parenchyma cells are round and they 
are compactly arranged (Fig. 3) on the upper side of the leaf, 
but on the under side they are arranged in round, small, intercel- 
lular spaces (Fig. 5). In some of the intercellular spaces are 
rosette crystals (Fig. 7). 

Under Epidermis. The under epidermal cells are smaller 
than the upper epidermal cells. 

It will be seen that the structure of trailing arbutus leaf is 
very simple and that its structure is different from that of klip 
buchu and mountain laurel. 

The structure of powdered leaves is very variable, yet char- 
acteristic for a given species. The leaves from the insect flower 
plant are collected with the stems, and ground and sold as a 



PLATE no 




Cross-Section Mountain Laurel (Kalmia latifolia, L.) 

i. Hair. 2. Epidermis. 3. Palisade parenchyma. 4. Parenchyma. 5. 
Under epidermis. 6. Intercellular space. 7. Rosette crystal. 8. Chlorophyll, 



PLATE in 




Cross-Section Trailing Arbutus Leaf {Epigcea repens, L.) 



I. Stomata. 2. Epidermis. 3. Parenchyma. 4. Cell with chlorophyll. 
5. Intercellular space. 6. Under epidermis. 7. Rosette crystal. 



LEAVES 



267 



substitute for insect flowers. These leaves, when powdered, 
show the following structure (Plate 112): 

Both the upper and lower epidermis have stomata (Figs. 
1 and 2), but they differ in that the surrounding cells of the 
upper epidermis are wavy, while the corresponding cells of the 
under epidermis are similar, though the under epidermis has 
many attached hairs (Figs. 3 and 4). The T-shaped hairs form 
the most abundant element of the powder. They are similar 
in structure to those found on the scales and stem. Fragments 
of the mesophyll have round cells and contain chlorophyll 
(Fig. 6). The conducting cells are spiral or reticulate. 

The different cells of the leaf differ greatly in structure, in 
amount, and in arrangement. In uva-ursi, boldus, pilocarpus, 
eucalyptus, and chimaphila leaves the outer walls of the epidermal 
cell is very thick. In uva-ursi leaves this thick wall appears 
bluish green when viewed under low power of the microscope. 

In belladonna, stramonium, henbane, peppermint, spear- 
mint, digitalis, and horehound, the outer wall of the epidermal 
cells is thin. 

In witch-hazel, stramonium, coca, phytolacca, and pepper- 
mint there is a single layer of palisade parenchyma on the 
upper surface only of the leaf. 

In senna there is one layer of palisade parenchyma on 
the upper and one layer on the under side of the leaf. In 
matico and tea leaves there are two, layers of spongy parenchyma 
on the upper side of the leaf. 

In chestnut leaves there are three layers of palisade paren- 
chyma on the upper side of the leaf. 

In eucalyptus leaves the entire central part of the leaf, 
with the exception of the secretion cells and fibro-vascular 
bundle, is made up of the palisade parenchyma. 

In some leaves no palisade parenchyma occurs. Trailing 
arbutus (Plate in) is an example of such a leaf. 

In stramonium leaves the spongy parenchyma is strongly 
branched; in mountain laurel the spongy parenchyma is 
mostly non-branched and circular in form, as in trailing arbutus 
(Plate in, Fig. 3), and as occurs in the midrib portion of most 
leaves. 

In stramonium and chestnut are found rosette crys- 



PLATE 112 




Powdered Insect Flower Leaves 
{Chrysanthemum cinerariifolium [Trev.], Vis.) 
i. Upper epidermis. 2. Under epidermis showing stoma and hair scar. 
3. Cross-section of under epidermis with attached hair. 4. Cross-section of 
upper epidermis. 5. Hairs. 6. Mesophyli with chlorophyll bodies. 7. Con- 
ducting cells. 



LEAVES 



269 



tals. In henbane, coca, and senna are found prisms. In bella- 
donna, scapola, and tobacco leaves are found micro-crystals. 
In most leaves no crystals occur. In witch-hazel and tea 
leaves stone cells occur, but in most leaves there are no stone 
cells. In eucalyptus, thyme, jaborandi, buchu, rosemary, and 
white pine leaves are secretion cells; while in belladonna, 
stramonium cells occur. In senna and coca leaves are crystal- 
bearing fibres; most leaves do not have crystal-bearing fibres. 

In chimaphila and uva-ursi there are no outgrowths from 
the epidermal cells. 

In senna, witch-hazel, chestnut, and coca, numerous non- 
glandular hairs occur on the epidermis. In tobacco, belladonna, 
henbane, pennyroyal, peppermint, and spearmint both glandular 
and non-glandular hairs occur on the epidermis. 

When studying leaves there should be considered the ab- 
sence or presence of outgrowths and their nature; the nature of 
the epidermis and, when present, the number of layers of the 
hypodermis; the nature of the stoma, whether raised above, 
even with, or below the level of the epidermis; the number of 
layers, and the distribution, when present, of the palisade 
parenchyma; the form and amount of the spongy parenchyma; 
the absence or presence of secretion cells; the nature and form 
of the fibro-vascular bundles, and the nature and amount of 
the organic and inorganic cell contents. 



CHAPTER VII 



FLOWERS 

The histological structure of flowers is readily seen in the 
powder; therefore, in studying flowers, it is not necessary to 
section the various parts. Each part of the flower should be 
isolated and powdered separately and each separated part 
studied. In each case the powders will contain surface, cross-, 
and radial sections of the parts powdered. While studying 
flowers, special attention should be given to the pollen grains, 
to the papillae of the petals, to the papillae of the stigma, and, 
in certain flowers, to the style tissue. In the composite flowers 
special attention should also be given to the involucre scales, 
to the scales of receptacle, and, when present, to the pappus. 
In addition, attention must be given to secretion cavities, as 
in cloves. 

POLLEN GRAINS 

Pollen grains are one of the most characteristic elements 
found in powdered flowers, because they are so small that they 
are not broken up when the drug is milled. 

The two principal groups of pollen grains are, first, those with 
non-spiny walls (Plate 113); and, secondly, those with spiny 
walls (Plate 114), as shown in the two charts. 

In lavender flowers the pollen grains have six constrictions 
of the outer wall. This wall is slightly striated and the cell 
contents are granular. 

In clover flowers the pollen grains are mostly rounded in 
outline, the wall is uniformly thickened, and cell contents are 
coarsely granular. 

In belladonna flowers the pollen grains terminate in three 
blunt points. 

In Spanish saffron the pollen grains are spherical and the 
cell contents are granular. 

270 



PLATE 113 




Smooth-walled Pollen Grains 

1. Cloves {Eugenia caryophyllata, Thunb.). 2. Santonica (Artemisia 
pauciftora, Weber). 3. Elder (Sambucus canadensis, L.). 4. Century minor 
(Erythrcea centaurium [L.], Pers.). 5. Pichi (Fabiana imbricata, R. and P.). 
6. Cyani. 7. Lavender (Lavandula officinalis, Chaix.). 8. Clover (Trifolium 
pratense, L.). 9. Belladonna (Atropa belladonna, L.). 10. Spanish saffron 
{Crocus sativus, L.). 



PLATE 114 




6 

Spiny Walled Pollen Grains 

Anthemis (Anthemis nobilis, L.). 
Arnica (Arnica montana, L.). 
Calendula (Calendula officinalis, L.). 
Cassia flowers. 

American saffron (Carthamus tinctorius, L.). 
Blue malva flowers (Malva sylvestris, L.). 



FLOWERS 



273 



The non-spiny- walled pollen grains differ not only in micro- 
scopic appearance, but also in size. Clove pollen grains are 
the smallest, while Spanish saffron pollen grains are the largest. 

NON-SPINY- WALLED POLLEN GRAINS 

In cloves the pollen grains show a six-sided, angled cavity 
and an outer wall which terminates in three slightly pointed, 
narrowly notched portions, separated by nearly straight walls. 

In santonica the pollen grains have smooth, unequally 
'thickened walls, which are strongly constricted at three points, 
the outline resembling three half-circles placed together. 

In elder flowers the pollen grains appear circular or three- 
parted. The wall is of nearly uniform thickness, even at the 
constricted part of the grain. 

In century minor the pollen grains show three pronounced 
restrictions. The wall at these points is very thin. In pichi 
flowers the pollen grains are either circular or three-sided and 
three-pointed. Inside of each point there is a nearly white pore. 
In some of the grains the pollen tube has grown out of one of 
the pores. 

In cyani flowers tne pollen grains are longer than broad and 
the cell contents appear to be divided into two end portions 
and an elevated middle portion 

SPINY- WALLED POLLEN GRAINS 

In anthemis the pollen grains have unequally thickened 
walls constricted in three places. The spines are short, broad 
at the base, and sharp-pointed. 

In arnica flowers the pollen grains show three light-colored 
pores and numerous short spines. 

In calendula flowers the pollen grains show one or more 
pores, typically three pores. These pores appear as white spots, 
and the wall immediately over the pore is smooth and thinner 
than the remaining part of the wall; the spines are very numerous. 

In cassia flower pollen grains the outer wall is extended into 
a number of rounded projections which are frequently arranged 
in sets of fours. 

In American saffron flowers the pollen grains show one, two, 
or three light-colored pores; the spines are short and broad. 



274 



HISTOLOGY OF MEDICINAL PLANTS 



In blue malva flowers the pollen grains are spherical and the 
outer wall extends into numerous spinelike projections. 

It will be observed that the spiny- walled pollen grains differ 
greatly. in size, the smallest being the pollen grain of anthemis 
and the largest being the pollen grain of blue malva 
flowers. 

In matricaria are numerous, greenish-brown, spiny-walled 
pollen grains. In anthemis are multicellular, uniseriate non- 
glandular hairs with three or four short, broad, yellow- 
walled basal cells and a greatly elongated, thin, gray-walled 
apical cell. 

In arnica are multiseriated branched hairs of the pappus, 
and numerous large, yellowish, spiny- walled pollen grains. 

STIGMA PAPILLiE 

The papillae of the stigma of most flowers form a character- 
istic element even when the flower is powdered. In the case 
of composite flowers the papillae of the disk and ray flowers 
differ. In American saffron the papillae of the style differ in a 
recognizable way from the papillae of the stigma. 

The papillae of the stigma of the ray and disk flowers of 
arnica, anthemis, matricaria, and insect flowers differ greatly. 
Even the papillae of the stigma of the ray and disk flowers differ. 
In all cases observed the papillae of the ray flowers are smaller 
than the papillae of the disk flowers. 

The papillae of the stigma of saffron (Plate 115, Fig. 3) are 
long and tubular. These papillae are nearly uniform in diam- 
eter, and the apex is blunt and rounded. The wall is slightly 
granular in appearance. The papillae of the stigma of American 
saffron (Plate 116, Fig. 2) are short and tubular. Each papilla 
is broadest at the base and tapers to a slender point. The 
papillae of that part of the style which emerges from the corolla 
(Plate 116, Fig. 1) are large and curved, and the walls are very 
thick. The apex of the papilla is frequently solid. 

The papillae of the stigma of the ray flowers of anthemis 
(Plate 117, Fig. 1) have thin, slightly striated walls; while the 
papillae of the stigma of the disk flowers (Plate 117, Fig. 2) are 
longer, the walls are thicker, and the cell content is denser. 

The papillae of the stigma of the ray (Plate 117, Fig. 3) and 



PLATE 115 




Papilla 

1. Arnica ray flowers (Arnica montana, L.). 

2. Insect flower disk (Chrysanthemum cinerariifolium [Trev.], Vis.). 

3. True saffron (Crocus sativus, L.) 



• 



PLATE 116 




Papilla of Stigmas 

1. Stigma papillae of American saffron (Carthamus tinctorius, L.) from that 
part of the style that emerges from the corolla. 

2. Papillae from the upper part of the stigma of American saffron. 

3. Papillae of the stigma of the disk flowers of arnica {Arnica montana, L.). 



PLATE 117 




Papilla of Stigmas 



1. Stigma papillae of the ligulate flowers of anthemis (Anthemis nobilis, L.). 

2. Stigma papillae of the tubular flowers of anthemis. 

3. Stigma papillae of the ligulate flowers of matricaria (Matricaria chamo- 
milla, L.). 

4. Stigma papillae of the disk flowers of matricaria. 

5. Stigma papillae of the ligulate flowers of insect flower (Chrysanthemum 
cinerariifolium [Trev.], Vis.). 



278 



HISTOLOGY OF MEDICINAL PLANTS 



disk flowers (Plate 117, Fig. 5) of matricaria are similar in 
structure, but the papillae of the disk flowers are larger. 

The papillae of the stigma of the. ligulate flowers of insect 
flowers (Plate 117, Fig. 5) are tubular; the walls are striated, 
and in each papilla there is a small yellow globule, while the 
papillae of the disk flowers (Plate 115, Fig. 2) are long and 
tubular, and the walls are thick. 

The papillae of the stigma of the ray flowers of arnica (Plate 
115, Fig. 1) are very short and tubular. The walls are thin 
and the cell contents appear as small, bright-yellow globules, 
while the papillae of the stigma of the disk flowers (Plate 116, 
Fig. 3) are broadest at the base, the apex is pointed, and the 
yellow globules are larger. 

The solitary hairs are divided into the branched and non- 
branched hairs. 

POWDERED INSECT FLOWERS 

The microscopic examination of insect powder is difficult for 
the reason that there are so many elements to be constantly 
kept in mind. The parts of the flower which contribute char- 
acteristic cells are the stem, involucre, ray flowers, disk flowers, 
and the receptacle. In each of these parts there are many 
different types of cells. 

There are practically two types of flowers found in insect 
powder of commerce: first, closed or immature flowers, and 
secondly, open or mature flowers. As explained above, the 
half-open flowers consist largely of the two above-named varie- 
ties. Let us first consider the structure of the closed insect 
flowers as illustrated in Plate 118. 

The involucre has many characteristic cells. The more 
prominent ones seen in the powder are the edge of the scale with 
the attached hair (Fig. 1). These hairs (Fig. 3) are T-shaped. 
The terminal cell is expanded laterally, and it terminates in 
two points. Connecting the terminal cell with the epidermis 
are two or three cells which are slightly longer than broad. 
In the powder the terminal cell is usually attached to fragments 
only of the supporting cells. Fibres of the bracts have thick, 
wavy, porous walls, and they have a tendency to occur in masses. 
The upper epidermis (Fig. 4) of the ray-flower petal is promi- 



PLATE 118 




Powdered Closed Insect Flower 
{Chrysanthemum cinerariijolium, [Trev.] Vis.) 

I. Edge of scale. 2. Fibre of scale. 3. Hairs. 4. Upper epidermis of 
ray flower. 5. Under epidermis of ray flower. 6. Cross-section of ray petal. 
7. Parenchyma of ray flowers with crystals. 8. Lobe of disk petal. 9. Filament 
tissue. 10. Calyx tissue. 11. Lobe of stamen. 12. Pollen. 13. Papillae of 
stigma. 14. Secretion cavity with surrounding cells. 15. Parenchyma of 
the receptacle. 



280 



HISTOLOGY OF MEDICINAL PLANTS 



nently papillate. The under epidermis consists of wavy cells 
without papillae. Another view of . the papillae is shown in 
Fig. 6. The parenchyma of the ray flowers (Fig. 7) contain 
cubical crystals. The lobe of the disk-flower petal (Fig. 8) 
is papillate at the end, the terminal cells have thick outer and 
thin inner walls. The filament tissue (Fig. 9) is composed of 
nearly square cells. The calyx tissue (Fig. 10) is made up of 
thin-walled cells with slightly papillate margins. The lobe of the 
stamen (Fig. 11) consists of nearly uniform epidermal cells 
which are in contact throughout their long diameter, while the 
hypodermal cells are thin- walled and angled. The pollen grains 
(Fig. 12) are dark yellowish green, thin, and the wall does not 
appear perforated by pores. The papillae of the stigma (Fig. 13) 
are clustered, club-shaped, and nearly white in color. They 
are usually found detached in the powder. All parts of the 
pistil contain secreting cells, but the most conspicuous secreting 
cavities (Fig. 14) are those of the ovary. These cavities appear 
brownish in color and are surrounded by small cells which appear 
indistinct on account of the great number of superimposed cells. 
The parenchyma of the receptacle occurs in fragments which 
have strongly marked porous walls. 

OPEN INSECT FLOWERS 

Many of the structures of open insect flowers (Plate 119) 
are similar to those found in the closed flower. There is prac- 
tically no difference in the edge of the scale (Fig. 1); or the 
fibre of the scale (Fig. 2) ; or the T-shaped hairs (Fig. 3) ; or the 
upper epidermis of the ray flower (Fig. 4) ; or the under epidermis 
of the ray flower (Fig. 5) ; or the cross-section of the ray petal 
(Fig. 6); or the lobe of the disk petal (Fig. 7); or the filament 
tissue (Fig. 8) ; or the lobe of the stamen (Fig. 9) ; or the papillae 
of the stigma (Fig. 12); or the parenchyma of the receptacle 
(Fig. 15). The difference in structure is found, first, in the 
involucre scales, which are more fibrous than the scales of the 
closed flowers; secondly, in the pollen (Fig. 11), which is less 
abundant than in the closed flower; it is also lighter in color 
and usually shows the wall perforated by three pores; thirdly, 
the outer layers of the achene consist of thick, porous-walled 
stone cells (Fig. 13), which occur singly or in groups; fourthly, 



PLATE 119 




Powdered Open Insect Flower 
{Chrysanthemum cinerariifolium, [Trev.] Vis.) 

I. Edge of involucre scale. 2. Fibres of involucre scale. 3. Hairs. 
4. Upper epidermis of ray flower. 5. Under epidermis of ray flower. 
6. Cross-section of ray petal. 7. Lobe of disk flower. 8. Filament tissue. 
9. Lobe of stamen. 10. Calyx tissue. 11. Pollen. 12. Papillae of the stigma. 
13. Stone cells from the achene and cross-section of achene. 14. Secretion 
cavity with surrounding cells. 15. Parenchyma of the receptacle. 



282 



HISTOLOGY OP MEDICINAL PLANTS 



the secretion cavity is broader and darker in color (Fig. 14). 
These differences enable one at once to distinguish between 
the closed and open insect flowers. Now, since the half -closed 
flowers consist almost wholly of a mixture of equal parts of 
closed and open flowers, it follows that the elements of these 
two flowers will be mixed in about equal proportions. Thus 
we are able to distinguish microscopically the three commercial 
varieties of insect powder — namely, closed insect flowers, open 
insect flowers, and half-open insect flowers. 

Insect flowers are the most valuable vegetable insecticide 
known ; yet much of its effectiveness is destroyed by the adulter- 
ants which are so readily identified by the compound microscope. 

POWDERED WHITE DAISIES 

A common adulterant found in open insect flowers is the 
flower-heads of European daisy (C. leucanthemum). Examination 
of powdered flowers exported from Europe shows that the entire 
flower-head is ground and mixed with the insect flowers. In 
the cheaper varieties of open flowers, only the tubular flowers 
are added after they have been separated from the heads by 
crushing and sifting. These tubular flowers so closely resemble 
the tubular flowers of the true insect flowers that it is practically 
impossible to distinguish between them macroscopically. The 
quickest and surest way to identify them is to reduce a portion 
of the flowers to a fine powder and examine it microscopically. 

Certain structures of the white daisies (Plate 120) are some- 
what similar to those found in insect flowers. These structures 
are the papillae of the ray petal (Figs. 3,5, and 13), the lobe of 
the disk petal (Fig. 14), and the lobe of the stamen and the 
pollen (Fig. 8). 

The differences are as follows: The under epidermis of the 
ray flowers is composed of wavy cells which are more elongated 
than the ray flowers of the under epidermis of the ray petal of 
insect flower. The filament tissue is made up of slightly beaded 
cells instead of smooth- walled cells. The papillae of the stigma 
are smaller than the papillae of insect flowers. The most striking 
difference is found in the structure of the achene. The epidermal 
tissue of the achene is composed of palisade cells (Fig. 10), which 
in the mature form have thick white walls and scarcely any 



PLATE 120 




Powdered White Daisies {Chrysanthemum leucanthemum, L.) 

i and 2. Scale tissue. 3, 5 and 13. Papillae of petals. 4. Scale tissue. 
6. Lobe of ray petal. 7. Filament tissue. 8. Pollen. 9. Papillae of stigma. 
10. Palisade cells of achene. II. Resin masses. 12. Parenchyma of recep- 
tacle. 14. Lobe of dish petal. 



284 



HISTOLOGY OF MEDICINAL PLANTS 



cavity. These cells swell perceptibly when placed in water. 
The other striking feature of the achene is the bright red resin 
masses which occur free in the field. Even a small trace of 
daisies in insect powder can be identified. 

When studying flowers there should be considered the number 
and structure of pollen grains; the nature of the papillae of the 
stigma and the petals; the nature of the hairs of the corolla and 
calyx, when present. In the composite flowers we should also 
consider the structure of the involucre scales, and, when present, 
the structure of the receptacle scales, as in the case of anthemus, 
and of the pappus hairs, as in the flowers of arnica, boneset^ 
grindelia, and aromatic goldenrod. 



CHAPTER VIII 



FRUITS 

There is great variation in the structure of fruits, such a 
variation, in fact, that no one fruit has a structure typical of 
all the other fruits. Each fruit, however, has a pericarp and 
one or more seeds. The amount and structure of the cells 
forming the pericarp and the seeds of fruits differ in different 
fruits, but for each fruit there is a normal amount of, and a 
characteristic, cellular structure. Nearly all the important 
medicinal fruits are cremocarps or umbelliferous fruits. 

The plan of structure of cremocarps is similar, but they all 
have a different cellular structure. The epidermis may be 
simple or modified as papillae or hairs. The secretion cavities 
may be absent (conium), or, when present, variable in number 
— cultivated celery seed has six, wild celery seed up to twelve, 
and anise up to twenty. The vascular bundles may be large or 
small. The endocarp cells may be two or more layers in thick- 
ness. The spermoderm may be thin or thick. 

The endosperm cells may vary in size and the cell contents 
may vary. 

CELERY FRUIT 

The fruit of celery (Plate 121), like other umbelliferous 
fruits, is composed of the pericarp and the seed. 

The pericarp is composed of epicarp cells, mesocarp cells, 
endocarp cells, and in each rib a vascular bundle. The seed is 
composed of the spermoderm, endosperm, and embryo. Each 
of these parts has a characteristic structure. 

Epicarp. The cells of the epicarp (Fig. 1) are papillae and the 
outer wall is striated. The papillae do not show, however, unless 
the cell is cut across the centre, which is the point at which the 
papillae are located. 

Mesocarp. In the rib part of the mesocarp (Fig. 2) is a 

285 



PLATE 121 




Cross-Section of Celery Fruit (Apium graveolens, L.) 

I. Epicarp. 2. Mesocarp. 3. Vascular bundle. 4. Endocarp. 
5. Spermoderm. 6. Endosperm. 7. Secretion cavity. 



PLATE 122 




Diagrammatic Drawing of the 
Cross-section of wild celery seed (Apium graveolens, L.). 
Cross-section of cultivated celery seed {Apium graveolens, L.) 



288 



HISTOLOGY OF MEDICINAL PLANTS 



vascular bundle, and between the ribs one or more secretion 
cavities. The vascular bundles are small and are surrounded by 
irregular-shaped mesocarp cells. 

The secretion cavities (Fig. 7) are oval in form and the tissue 
bordering the cavity is reddish brown in color. The mesocarp 
cells around the secretion cavities are more elongated than the 
other mesocarp cells. 

Endocarp. The endocarp ceils are three layers in thickness. 
These cells are elongated transversely (Fig. 4). 

Spermoderm. The cells of the spermoderm are indistinct, 
compressed, and dark brown in color (Fig. 5) . 

Endosperm. The endosperm cells (Fig. 6) make up the greater 
part of the fruit. The walls which are common to two cells 
are thick, non-beaded, and non-pitted, and the cavities of the 
cells are filled with aleurone grains. 

Embryo. The embryo cells, which show only in certain 
sections, are similar to endosperm cells. 

In .anise, hops, sumac, and cumin fruits are characteristic 
hairs. 

In star anise, sabal, allspice, cubeb, pepper, juniper, buck- 
thorn, and phytolacca fruits are stone cells. 

In cubeb, pepper, and cardamon are characteristic masses of 
aggregate starch. 

In sabal, allspice, and juniper are characteristic secretion cells. 

In all the umbelliferous fruits, with the exception of conium, 
are yellow to brown secretion cavities. 

In cubeb and pepper is aggregate starch. Colocynth con- 
tains many single and double spiral vessels. 

Bitter orange contains solitary crystals and spongy par- 
enchyma. 

When studying fruits we must consider the nature of the 
epicarp cells — whether simple or modified as papillae or hairs; 
the form and structure of the mesocarp cells; the number, size, 
and structure of the vascular bundle; the size and number of 
the secretion cells or cavities; the number of layers and the 
structure of the endocarp cells; the number of layers of stone 
cells — when present; the color and width of the spermoderm 
layer; the structure and cell contents of the endosperm cells; 
the nature of the embryo cells, and the nature of the cell contents. 



CHAPTER IX 



SEEDS 

Seeds are very variable in structure, so much so, in fact, 
that scarcely any two seeds have a similar structure. It is 
necessary, therefore, when examining seeds, to compare the struc- 
ture of the seed under examination with authentic plates or 
with the section of a genuine seed. The layers of the seed 
are the spermoderm, perisperm, endosperm, and embryo. In 
some seeds the spermoderm forms the greater part of the seed; 
in others the perisperm is greatest in amount; in still others 
the cotyledons make up most of the seed, as in the mustards. 
The cells forming these different layers differ in form, structure, 
and number; therefore it is not difficult to distinguish and to 
differentiate between the different seeds when viewed as a sec- 
tion or as a powder. Almond is studied because it has most of 
the layers and cells found in seeds. 

SPERMODERM 

The spermoderm is the thin, brown, granular-appearing 
skin of the almond. The layers of the spermoderm are the 
epidermis, the hypoderm, the middle layers, and the inner 
epidermis. 

The epidermis consists of radially elongated, thick-walled 
stone cells which occur alone or in groups of two or more, but 
seldom as a continuous layer. The upper or outer part of the 
stone cells is non-porous, but the inner walls are strongly porous 
(Plate 123, Fig. 1). 

The hypoderm. The cells forming the hypoderm are com- 
pressed, the wall structure is practically indistinguishable, and 
the whole mass is reddish brown (Plate 123, Fig. 2). 

Occurring in this brown layer are several vascular bundles 
(Plate 123, Fig. 3). 

289 



PLATE 123 




Cross-Section Sweet Almond Seed 



1. Epidermis. 2. Hypoderm. 3. Vascular bundle. 4. Middle layer. 
5. Inner epidermis. 6. Endosperm. 7. Outer layer of the embryo. 8. Inner 
layers of the embryo. 



SEEDS 



291 



The middle layers. The cells forming the middle layers 
(Fig. 4) have thin, wavy, light-colored walls which are frequently 
compressed, and it is with much difficulty that their outlines 
are made out. 

The inner epidermis. The cells forming the inner epidermis 
are rectangular in form, and they contain reddish-brown cell 
contents (Plate 123, Fig. 5). 

ENDOSPERM 

The endosperm. The cells forming the endosperm are large, 
rectangular in outline, usually one layer thick, and they contain 
aleurone grains. 

EMBRYO 

The embryo. The cells forming the outer layer of the em- 
bryo are smaller than the inner layers, and they are immediately 
inward from the layer of endosperm cells (Plate 123, Fig. 7). 

The cells forming the greater part of the embryo are large, 
rounded, and they contain aleurone grains and fixed oil (Plate 
123, Fig. 8). 

In white and black mustard are characteristic mucilage and 
palisade cells. 

In nux vomica, stropanthus, and St. Ignatius's bean are 
characteristic hairs. 

In physostigma and kola are characteristic starch grains. 

In henbane, capsicum, stramonium, lobelia, and belladonna 
seeds are characteristic epidermal cells. 

In areca nut, colchicum, saw palmetto, and nux vomica are 
characteristic thick- walled, reserve cellulose cells. 

In cardamon seed are aggregate starch masses with irregular 
outlines. 

In bitter and sweet almond, linseed, pepo, and stropanthus 
are aleurone grains. 

In bitter and sweet almonds are stone cells. 

In linseed, quince seed, and in white and black mustard are 
epidermal cells with mucilaginous walls and contents, etc. 



CHAPTER X 



ARRANGEMENT OF VASCULAR BUNDLES 

Having familiarized ourselves with the different types of 
mechanical and conducting cells, we shall now consider the 
different ways in which these cells are associated to form the 
vascular and ribro-vascular bundles. 

The simplest form of the vascular bundle occurs in petals, 
floral bracts, and leaves. In these parts the vascular bundle 
is made up of conducting cells only. 

In the great majority e»f cases, however, the conducting cells 
are associated with mechanical cells to form the ribro-vascular 
bundle. 

The ribro-vascular bundle is made up of, first, the phloem, 
which consists of sieve tubes, companion cells, bast fibres, and 
parenchyma; secondly, of the xylem, composed of vessels and 
tracheids, wood fibres and wood parenchyma; thirdly, of medul- 
lary rays (restricted to certain types); and fourthly, of the 
bundle sheath (restricted to certain types). 

TYPES OF FIBRO-VASCULAR BUNDLES 

There are three well-defined types of the fibro-vascular 
bundle, namely, the radial, the concentric, and the collateral 
types. 

RADIAL VASCULAR. BUNDLES 

The radial type of bundle is met with most frequently in 
monocotyledonous roots. 

In this form (Plate 114) the xylem forms radial bands of 
tissue which alternate with isolated groups of phloem. The 
space between the phloem and xylem is filled in with either 
parenchyma or fibres, or both. In some cases the vessels of 
the xylem meet in the centre of the root, while in other cases 

292 



PLATE 124 




Cross-Section of a Radial Vascular Bundle of Skunk Cabbage Root 
(Symplocarpus fcetidus [L.], Nutt.) 

1. Vessels. 

2. Bundle sheath. 

3. Parenchyma. 

4. Sieve cells. 



PLATE 125 




Cross-Section of a Phloem-Centric Bundle of Calamus 
Rhizome (Acorus calamus, L.) 

1. Vessels. 

2. Sieve cells. 

3. Phloem parenchyma. 

4. Parenchyma surrounding the bundles. 



ARRANGEMENT OE VASCULAR BUNDLES 



295 



the centre of the stem is occupied by pith parenchyma. Each 
bundle is surrounded by parenchyma cells, and in iris, calamus, 
and veratrum, rhizomes, and endodermis, surrounds the bundles 
located in the centre of the stem, consisting of thin-walled 
(mechanical) cells. 

In sarsaparilla root, the pith is composed of thick-walled, 
porous pith parenchyma cells with starch. Outside the pith 
are arranged radial bands of oval vessels which decrease in size 
toward the periphery. Between the ends of these bands occur 
isolated groups of sieve cells. 

Surrounding the sieve cells and vessels are thick-walled, 
angled fibres. 

External to these cells is an endodermis composed of lignified 
brownish- colored cells one layer in thickness. 

CONCENTRIC VASCULAR BUNDLES 

There are two principal types of the concentric bundle, 
namely, xylem-centric, in which the xylem is centric and the 
phloem is peripheral, as in veratrum root; and phloem- centric 
(Plate 125), in which the phloem is centric and the xylem pe- 
ripheral, as in calamus rhizome. 

COLLATERAL VASCULAR BUNDLES 

There are three types of collateral vascular bundles — namely, 
closed collateral, bi-collateral, and open collateral. 

In the closed collateral bundle the phloem and xylem are 
not separated by a cambium layer, and in many cases the 
bundle is surrounded by thick, angled walled fibres, as in palm 
stem. The term closed bundle refers to the fact that there is 
no cambium between the xylem and phloem, therefore the 
bundle is "closed" to further growth, and not to the fact that 
it is frequently surrounded by fibres which prevent further 
growth. In podophyllum stem (Plate 126) the xylem portion 
of the bundle faces the centre of the stem and the phloem portion 
of the bundle faces the epidermis. The xylem and phloem are 
separated by a cambium layer, and both are surrounded by 
thick-walled angled fibres which are the chief mechanical cells 
of the stem. This bundle is, in fact, mechanically closed, but 
not physiologically because a cambium is present. 



PLATE 126 




Cross-Section of a Closed Collateral Bundle of Mandrake Stem 
{Podophyllum peltatum, L.) 

1. Vessels. 

2. Sieve cells. 

3. Cambium. 

4. Fibres. 

5. Parenchyma. 

6. Intercellular space. 



PLATE 127 




Bl-COLLATERAL BUNDLE OF PUMPKIN STEM (CurCUrbitd pepO, L.) 

1. Vessels. 

2. Sieve tubes. 



298 



HISTOLOGY OF MEDICINAL PLANTS 



BI-COLLATERAL VASCULAR BUNDLES 

In the bi-collateral vascular bundle (Plate 127) the xylem is 
in between two groups of phloem — namely, an inner group and 
an outer group. 

In pumpkin stem a bundle occurs in each angle of the stem. 
The entire bundle is surrounded by parenchyma cells. 

In an individual bundle the xylem consists of large circular 
vessels and a phloem containing large sieve cells, many of 
which show the yellow porous sieve plates. 

OPEN COLLATERAL VASCULAR BUNDLES 

In the open collateral bundle (Plate 100) the xylem and 
phloem are separated by the cambium layer, which, through 
its divisions, causes the stem to increase in thickness each year. 
This type of bundle is characteristic of the stems and roots of 
dicotyledonous plants. 

The bi-collateral bundle occurs in many leaves. The xylem 
in such cases is central, the phloem strands occupying upper 
and lower peripheral positions. 



INDEX 



Abbe condenser, illustration, 1 1 
Absorption tissue, introduction, 12 1 

tissue of leaves, 125 
Aerating tissue, introduction, 151 
Annular vessels, illustration of, 129 
Bark, of white pine powdered, de- 
scription of, 250 

of white pine powdered, illustra- 
tion of, 251 

unrossed white pine, cross-sec- 
tion, illustration of, 249 
Barks, description of, 248 

diagnostic structures of, 253 

structural variations of, 252 
Base sledge microtome, 35 

sledge microtome, illustration, 35 
Bast fibres, 89 

branched, 92 

branched, illustrations, 95 
crystal bearing, 90, 92 
description of, 100 
groups of, illustrations, 102 
non-porous and non-striated, 96 
non-porous and non-striated, il- 
lustrations, 1 01 
non-porous and striated, 96 
occurrence in powdered drugs, 
103 

of barks, illustrations, 91, 93, 94 

of klip buchu leaf, 262 

of ruellia rhizome, 226 

of ruellia root, 223 

of ruellia stem, 235 

of spigelia stem, 235 

porous and non-striated, illus- 
trations, 98 

porous and striated, 92 

porous and striated, illustrations, 
97 

storage function of, 179 
striated and non-porous, illus- 
trations of, 99 



Bi-collateral vascular bundles, de- 
scription of, 298 
Buchu stems, cross-section, illustra- 
tion of, 243 

cross-section, illustration of, 244 

powdered, description of, 245 

powdered, illustration of, 246 
Cambium of pink root, 221 

of ruellia rhizome, 226 

of ruellia stem, 237 

of spigelia rhizome, 223 

of spigelia stem, 235 
Camera lucida, 22 

illustrations, 22 
Care of microscope, 28 
Celery fruit, diagrammatic drawing of, 
287 

Cell contents, 182 

aleurone grains, 197 
aleurone grains, description of, 
198 

aleurone grains, form of, 197 
aleurone grains, structure of, 197 
aleurone grains, tests for, 198 
chlorophyll, 182 
crystals, 200 

crystals, composition of, 200 
crystals, micro-, 200 
crystals, raphides, 200 
crystals, rosette, 200 
crystals, solitary, variation of, 
205 

cystoliths, 210 
cystoliths, forms of, 210 
cystoliths, occurrence of, 215 
cystoliths, tests for, 215 
hesperidin, 196 
hesperdiin, test for, 196 
inulin, 194 
inulin, tests for, 194 
leucoplastids, 183 
mucilage, 194 



299 



300 



INDEX 



Cell contents, mucilage associated 
with raphides, tests for, 194 
mucilage, tests for, 194 
organic, 182 

starch grains, formation of, 183 
starch grains, hilum nature of, 188 
starch grains, hilum of, 185 
starch grains, mounting of, 188 
starch grains, occurrence of, 184 
starch grains, outline of, 185 
starch grains, size of, 185 
starch grains, tests for, 188 
tannin, 196 

tannin, occurrence of, 196 
tannin, test for, 197 
volatile oil, test for, 196 
volatile oils, 196 
Cell division common to onion root, 
56 

Cell plate, 55 
Cell sap, 53 
Cell, typical, 53 
Cell wall, 53 
Chromatin, 54 
Chromatin granules, 55 
Chromatophores, 53 
Chromosomes, 55 

Closed collateral bundles of mandrake 
stem, cross-section illustration 
of, 296 

Collateral vascular bundles, 295 
Collenchyma cells, composition of 
walls, 109 
illustrations, 108 
occurring in catnip and mother- 
wort, illustrations, 107 
of ruellia stem, 235 
structure of, 106 
Compound microscope, illustration, 10 
microscope, mechanical parts of, 
7,8 

microscope of Robert Hooke, 

illustration, 8 
microscope, optical parts of, 9, 

11, 12 

microscopes, introduction, 7 
Concentric vascular bundles, 295 
Conducting tissue, introduction, 126 
Cork cells, origin of, 88 
Cortical parenchyma, conduction by, 
147 

of ruellia stem, 235 



Cortex, of pink root, 219 

of ruellia rhizome, 226 

of ruellia root, 221 

of ruellia stem, 235 

of spigelia rhizome, 223 

of spigelia stem, 233 
Cover glasses, 43 

illustrations, 44 
Crystal cavities, 176 

cells, storage function of, 179 
Cutting sections, 31 
Cystoliths, illustrations of, 214 
Cytoplasm, 53 

Daisies, white, powdered, description 
of, 282 

illustration of, 283 
Dissecting microscope, illustration, 5 

needles, 46 

needles, illustration, 46 
Drawing apparatus, illustration, 23 
Ectoplast, 53 

Embryo, diagnostic structures of, 
291 

Endocarp of celery fruit, 288 
Endodermal cells, illustrations of 
longitudinal sections, 119 
illustrations of cross-sections, 117 
introduction, 116 
structure of, 116, 118 
Endodermis, of klip buchu leaf, 
262 

of pink root, 219 

of ruellia root, 223 
Endosperm of celery fruit, 288 

of seeds, 291 
Epicarp of celery fruit, 285 
Epidermal cells of leaves, storage 

function of, 179 
Epidermis, surface deposits of, 62 

of herbaceous stems, illustra- 
tions of, 152 

of klip buchu leaf, 260 

of leaves, illustrations of, 155 

of mountain laurel, 264 

of pink root, 219 

of ruellia rhizome, 226 

of ruellia root, 221 

of ruellia stem, 235 

of seeds, 289 

of spigelia rhizome, 223 

of spigelia stem, 233 

of testa, 63 



INDEX 



301 



Epidermis of trailing arbutus, 264 
Equatorial plane, 55 
plate, 55 

Fibro-vascular bundles, composition 
of, 292 
of klip buchu leaf, 262 
types of, 292 
Flowers, diagnostic structures of, 
284 
parts of, 270 
Folding magnifier, 4 

illustration, 4 
Fruits, cellular structure of, 285 

diagnostic characteristics of, 
288 

diagnostic structures of, 288 
Glandular hairs of peppermint, 178 
illustrations of, 165 
multicellular, 164 
multicellular, multiseriate 

stalked, 166 
multicellular, multiseriate 

stalked, description of, 166 
multicellular, multiseriate 

stalked, occurrence, 166 
multicellular sessile, 164 
multicellular stalked, 164 
multicellular, uniseriate stalked, 

164 

stalked, illustrations of, 167 
storage function of, 178 
unicellular, 164 

unicellular, multiseriate stalked, 
164 

unicellular sessile, 164 
unicellular stalked, 164 
unicellular, uniseriate stalked, 
164 

Glandular tissue, introduction, 164 
Glass slides, 44 

illustrations, 44 
Greenough binocular microscope, 15 

illustration, 15 
Guard cells, 151 

Hairs, multicellular, multicellular 

non-branched, illustration, 75 
multicellular, multiseriate 

branched, of Shepherdia, 78 
multicellular, multiseriate 

branched, 77, 82 
multicellular, multiseriate 

branched, illustrations, 79, 81 



Hairs, multicellular, multiseriate non- 
branched, 74 

multicellular, uniseriate 
branched, illustration, 76 

multicellular, uniseriate n o n - 
branched, 72 

multicellular, uniseriate n o n - 
branched, illustrations of, 73 
Hand cylinder microtome, illustra- 
tion, 34 

microtome, 31 

microtome, illustration, 31 

table microtome, 34 

table microtome, illustration, 34 
Horehound, powdered, description of, 
237 

powdered, illustration of, 238 
spurious, powdered, description 
of, 237 

spurious, powdered, illustration 
of, 239 
Hypoderm of seeds, 289 
Hypodermal cells, of leaves, storage 
function of, 179 
illustrations, 120 
structure of, 118 
Hypoderms, of klip buchu leaf, 260 

of ruellia root, 221 
Illumination for microscope, 26 
Indirect cell division, 54, 55 
Inner bark of white pine, 248 

epidermis of seeds, 291 
Insect flower leaves, powdered, illus- 
trations of, 268 
stems, description of, 241 
stems, powdered, illustration of, 
240 

Insect flowers, closed, powdered, illus- 
tration of, 279 
open, description of, 280 
open, powdered, illustration of, 
281 

powdered, description of, 278 
Intercellular spaces, 158 

illustrations of, 160, 161 
Internal phloem, of spigelia stem, 235 
Inulin, illustrations of, 195 
Karyokinesis, 54, 55 
Klip buchu, cross-section, illustration 
of, 261 

powdered, description of, 262 
powdered, illustration of, 263 



302 



INDEX 



Labeling, 47 
Latex cavities, 176 

tube cavities, 176 

tubes, 142, 144 

tubes, illustration of, 145 

vessels, illustrations of, 146 
Leaf epidermis, 59 

illustrations, 60, 61 
Leaf parenchyma, conduction by, 150 
Leaves, diagnostic structures of, 267 

stomata, 260 
Lenticel, illustration of cross-section, 
159 

Lenticels, aerating function of, 157 

structure of, 158 
Linin, 54 

Long paraffin process, 29 
Machine microtomes, 32 
Measuring cylinder, 40 

illustration, 40 
Mechanical stage, 21 

stage, illustration, 22 

tissue, 89 
Medullary ray, 139 

bundle, 139 

bundle in tangential-section of 

quassia wood, 258 
cell, 141 

cell, arrangement of, in the ray, 
142 

cell, structure of, 142 

cells, in cross-section of quassia 
wood, 254 

cells, in radial-section of quassia 
wood, 258 

cells, in tangential-section of 
quassia wood, 258 

cells, of ruellia stem, 237 
Medullary rays, illustration of cross- 
sections of, 143 

illustration of longitudinal sec- 
tion, 140 

in cross-section of quassia wood, 

254 . 

in radial-section of quassia wood, 
254 

of pink root, 221 
of ruellia rhizome, 227 
of ruellia root, 223 
of spigelia rhizome, 226 
of white pine bark, 250 
Mesocarp of celery fruit, 285 



Method of mounting specimens, 41 
Micro-crystals, illustrations of, 201 

lamp, 27 
Micrometer eye-pieces, 21 

illustrations, 20, 21 
Microphotographic apparatus, 24 

illustration, 24 
Microscope, how to use, 25 
Microscopic measurements, 19 
Microtome> care of, 36 
Middle bark of white pine, 248 

lamella, 55 

layers of seeds, 291 
Minor rotary microtome, 36 

illustration, 36 
Mountain laurel, cross-section, illus- 
tration of, 265 
Mucilage cavities, 172, 176 
Multicellular hair, 72 
Nuclear membrane, 55 

spindle, 55 
Nucleoli, 55 
Nucleus, 53 

Objectives, illustrations, 11 
Ocular micrometer, 19 

illustration, 19 
Oil cavities, occurrence, 178 

of leaves, 178 

of seeds, 178 

unicellular, 172 
Open collateral vascular bundles, de- 
scription of, 298 
Origin of multicellular plants, 57 
Outer bark of white pine, 248 
Palisade parenchyma, conduction by, 
150 

Papillae, 67 

illustrations of, 275 
of stigmas, illustrations of, 276, 
277 

stigma, description of, 274 

Paraffin, blocks, 31 

embedding oven, illustration, 30 

Parenchyma, aquatic plant, 150 
cells of white pine, 248 
conduction by, 144 
cortical, illustrations of, 148 
of mountain laurel, 264 
of trailing arbutus, 264 
pith, illustrations of, 149 

Pericycle of pink root, 221 
of ruellia root, 223 



INDEX 



303 



Periderm, 80 
cork, 80 

illustrations of, 86 
of cascara sagrada, illustrations, 
84 

of white oak bark, illustration 
of, 87 

parenchyma and stone cells, 85 
stone cells, 85 
Permanent mounts, 41 
Pharmacognostic microscope, illus- 
tration, 12 
Phloem, centric bundle of calamus, 
cross-section, illustration of, 
294 

of ruellia rhizome, 226 
of ruellia stem, 235 
of spigelia rhizome, 223 
of spigelia stem, 233 
Phloem parenchyma, conduction by, 
150 

of pink root, 221 

of ruellia rhizome, 226 

of ruellia root, 223 

of ruellia stem, 235 

of spigelia rhizome, 223 

of spigelia stem, 235 
Photosynthetic tissue, 163 
Pink root, description of, 227 
Pith parenchyma, conduction by, 
147 

of pink root, 221 

of ruellia rhizome, 227 

of ruellia root, 223 

of ruellia stem, 237 

of spigelia rhizome, 226 

of spigelia stem, 235 
Pitted vessels, with bordered pores, 
illustration of, 135 

illustrations of, 134 
Plant hairs, forms of, 67 

introduction, 66 
Polar caps, 55 
Polarization microscope, 16 

illustration, 16 
Pollen grains, 270 

non-spiny-walled, description of, 
273 

smooth-walled, illustrations of, 
271 

spiny-walled, description of, 273 
spiny-walled, illustrations of, 272 



Preparation of specimens for cutting, 
28 

Protoplast, 53 

Quassia wood, cross-section, illustra- 
tion of, 255 

radial-section, illustration of, 257 
Radial vascular bundles, 292 

skunk cabbage root, cross-sec- 
tion, illustration of, 293 
Raphides, illustrations of, 203 
Reading glass, 4 

illustration, 4 
Reagent set, illustration, 39 
Reagents, list of, 38 
Research microscope, 13 

illustration, 14 
Reserve cellulose, illustrations of, 
I 80-181 

Reticulate vessels, illustrations of, 133 
Root hairs, 121, 122, 125 

illustration of, 123 

illustration of fragments, 124 
Roots and rhizomes, 219 

diagnostic structures of, 227 
Rosette and solitary crystals, illus- 
trations of, 213 

crystals, illustrations of, 204 

crystals, inclosed, illustrations of, 
206 

Ruellia ciliosa, Pursh., powdered, 
illustration of, 229 
ciliosa, Pursh., rhizome, cross- 
section, illustration of, 225 
ciliosa, Pursh., stem, cross-sec- 
tion, illustration of, 236 
root, description of, 227 
root, illustration of, 222 
Scalpels, 46 

illustration, 47 
Scissors, 46 

illustration, 46 
Sclariform vessels, illustrations of, 
132 

Seeds, parts of, 289 

Secretion cavities, of celery fruit, 288 

description of, 176 

illustrations of, 1 69-1 71 

introduction, 166 

lysigenous, 168 

schizogenous, 168 

schizo-lysigenous, 168 

unicellular, 168 



304 



INDEX 



Secretion cells, of klip buchu leaf, 262 

of white pine, 248 
Short paraffin process, 29 
Sieve cells, of klip buchu leaf, 262 

of pink root, 221 

of ruellia rhizome, 226 

of ruellia root, 223 

of ruellia stem, 235 

of spigelia stem, 235 
Sieve plate, 138 

illustration of, 137 
Sieve tube, illustration of, 137 

tubes, introduction, 136 

tubes, structure, 136 
Simple microscope, introduction, 3 
Slide box, 48 

box, illustration, 48 

cabinet, 49 

cabinet, illustration of, 49 
forceps, 45 

forceps, illustrations, 45 
tray, 48 

tray, illustration, 48 
Solitary crystals, illustrations of, 207- 
209, 211, 212 
unicellular hairs, 69 
Special research microscope, 14 

illustration, 14 
Specimens, preservation of, 48 
Spermoderm, of celery fruit, 288 

of seeds, 289 
Spigelia marylandica, powdered, il- 
lustration of, 228 
rhizome, cross-section, illustra- 
tion of, 224 
root, cross-section, illustration 
of, 220 

stem, cross-section, illustration 
of, 234 
Spindle fibres, 55 

Spiral vessels, illustrations of, 129, 
130 

Spongy parenchyma of klip buchu, 
260 

Stage micrometer, 19 

illustration, 19 
Staining dish, 40 

illustration, 40 
Standardization of ocular microm- 
eter, 19 

Starch grains, illustrations of, 186, 
187, 189-193 



Steinheil lens, 5 

illustration, 5 
Stems, diagnostic structures of, 233 

dicotyledonous, 233 

herbaceous, 233 

monocotyledonous, 233 
Stomata, aerating function of, 151 

illustrations of cross-section, 156 

relation to surrounding cells, 

154 

types of, 153 
Stone cells, of ruellia root, 223 
branched, 109 

branched, illustrations of, no 

description, in, 112 

introduction, 109 

occurrence, illustrations, 115 

porous and non-striated, in 

porous and non-striated, illus- 
trations of, 114 

porous and striated, 109 

porous and striated, illustrations 
of, 113 

storage function of, 178 
Storage cavities, 176 

cavities, illustrations of, 177 

cells, 173 

cells, cortical parenchyma, 173 
cells, illustrations of, 174 
cells, pith parenchyma, 173 
cells, wood parenchyma, 173 
tissue, 173 

walls, description of, 179 
Stored mucilage and resin, illustra- 
tions of, 175 
Surrounding cells, arrangement of, 
154 

Synthetic tissue, introduction, 163 
Temporary mounts, 41 
Testa cells, 65 

epidermal cells, illustrations, 64 
Tracheids of pink root, 221 
Trailing arbutus leaf, cross-section, 

illustration of, 266 
Tripod magnifier, 4 

illustration, 4 
Turntable, 46 

illustration, 47 
Under epidermis of klip buchu leaf, 
262 

epidermis of mountain laurel, 
264 



INDEX 



305 



Under epidermis of trailing arbutus, 
264 

hypodermis of klip buchu leaf, 
262 

palisade parenchyma of klip 
buchu leaf, 262 
Unicellular clustered hairs, 72 

clustered hairs, illustrations, 71 
non-glandular hairs, 69 
solitary branched hairs, 72 
solitary hairs, illustrations, 70 
Upper palisade parenchyma of klip 
buchu leaf, 260 
palisade parenchyma of moun- 
tain laurel, 264 
Vacuoles, 53 

Vascular bundles, arrangement of, 
292 

occurrence of, 292 
Vessels, annular, 127 

and tracheids, introduction, 126 
in cross-section of quassia wood, 
254 

in radial-section of quassia wood, 
254 

in tangential-section of quassia 

wood, 258 
of ruellia rhizome, 226 
of ruellia root, 223 
of ruellia stem, 237 
of spigelia rhizome, 226 
pitted, 131 

pitted with bordered pores, 131 
reticulate, 131 
sclariform, 128 
spiral, 127 



Water pores, aerating function of, 151 
Watchmaker's loupe, 4 

illustration, 4 
Wood fibres, color of, 104 

illustrations, 105 

in cross-section of quassia wood, 

254 . 

in radial-section of quassia wood, 

in tangential-section of quassia 

wood, 258 
introduction, 104 
structure of, 104 
Wood parenchyma, conduction by, 
150 

in cross-section of quassia wood, 
254 . 

in radial-section of quassia wood, 
258 

of pink root, 221 

of ruellia rhizome, 227 

of ruellia root, 223 

of ruellia stem, 237 

of spigelia rhizome, 226 

of spigelia stem, 235 
Woods, description of, 254 

diagnostic structures of, 258 
Woody stems, buchu stem, descrip- 
tion of, 242 

mature buchu stem, 242 
Xylem, of pink root, 221 

of ruellia rhizome, 226 

of ruellia root, 223 

of ruellia stem, 237 

of spigelia rhizome, 226 

of spigelia stem, 235 



